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 $87.59   8.813%   $95.3093   $95.31   $95.30   $95.30  
  Purchase #2 $218.47   6.779%   $233.2801   $233.28   $233.30   $233.30  
  Purchase #3 $154.90   10.150%   $170.6224   $170.62   $170.60   $170.60  
  Purchase #4 $247.63   12.659%   $278.9775   $278.98   $279.00   $279.00  
  Purchase #5 $185.32   7.529%   $199.2727   $199.27   $199.25   $199.30  
  Purchase #6 $73.35   4.736%   $76.8239   $76.82   $76.80   $76.80  
  Purchase #7 $177.67   9.205%   $194.0245   $194.02   $194.00   $194.00  
  7 purchase totals = $1,144.93       $1,248.3104   $1,248.30   $1,248.25   $1,248.30