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 $206.69   8.251%   $223.744   $223.74   $223.75   $223.70  
  Purchase #2 $139.87   4.182%   $145.7194   $145.72   $145.70   $145.70  
  Purchase #3 $76.64   6.719%   $81.7894   $81.79   $81.80   $81.80  
  Purchase #4 $12.60   12.233%   $14.1414   $14.14   $14.15   $14.10  
  Purchase #5 $151.64   10.424%   $167.447   $167.45   $167.45   $167.40  
  Purchase #6 $30.68   4.314%   $32.0035   $32.00   $32.00   $32.00  
  Purchase #7 $172.41   3.485%   $178.4185   $178.42   $178.40   $178.40  
  7 purchase totals = $790.53       $843.2632   $843.26   $843.25   $843.10