Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $41.25   12.277%   $46.3143   $46.31   $46.30   $46.30  
  Purchase #2 $221.84   10.833%   $245.8719   $245.87   $245.85   $245.90  
  Purchase #3 $116.74   5.451%   $123.1035   $123.10   $123.10   $123.10  
  Purchase #4 $26.79   5.304%   $28.2109   $28.21   $28.20   $28.20  
  Purchase #5 $184.52   12.692%   $207.9393   $207.94   $207.95   $207.90  
  Purchase #6 $160.43   10.335%   $177.0104   $177.01   $177.00   $177.00  
  Purchase #7 $92.35   4.791%   $96.7745   $96.77   $96.75   $96.80  
  7 purchase totals = $843.92       $925.2248   $925.21   $925.15   $925.20