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 $59.85   11.837%   $66.9344   $66.93   $66.95   $66.90  
  Purchase #2 $97.96   5.420%   $103.2694   $103.27   $103.25   $103.30  
  Purchase #3 $183.91   5.498%   $194.0214   $194.02   $194.00   $194.00  
  Purchase #4 $102.46   3.455%   $106   $106.00   $106.00   $106.00  
  Purchase #5 $45.27   4.221%   $47.1808   $47.18   $47.20   $47.20  
  Purchase #6 $214.26   5.368%   $225.7615   $225.76   $225.75   $225.80  
  Purchase #7 $26.93   4.582%   $28.1639   $28.16   $28.15   $28.20  
  7 purchase totals = $730.64       $771.3314   $771.32   $771.30   $771.40