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 $86.54   11.203%   $96.2351   $96.24   $96.25   $96.20  
  Purchase #2 $33.73   4.403%   $35.2151   $35.22   $35.20   $35.20  
  Purchase #3 $73.58   3.414%   $76.092   $76.09   $76.10   $76.10  
  Purchase #4 $14.44   9.690%   $15.8392   $15.84   $15.85   $15.80  
  Purchase #5 $235.52   5.246%   $247.8754   $247.88   $247.90   $247.90  
  Purchase #6 $110.90   3.575%   $114.8647   $114.86   $114.85   $114.90  
  Purchase #7 $114.31   8.770%   $124.335   $124.34   $124.35   $124.30  
  7 purchase totals = $669.02       $710.4565   $710.47   $710.50   $710.40