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 $64.26   13.766%   $73.106   $73.11   $73.10   $73.10  
  Purchase #2 $122.93   10.575%   $135.9298   $135.93   $135.95   $135.90  
  Purchase #3 $69.96   8.648%   $76.0101   $76.01   $76.00   $76.00  
  Purchase #4 $145.59   9.448%   $159.3453   $159.35   $159.35   $159.30  
  Purchase #5 $64.31   6.474%   $68.4734   $68.47   $68.45   $68.50  
  Purchase #6 $116.74   10.738%   $129.2755   $129.28   $129.30   $129.30  
  Purchase #7 $71.46   3.483%   $73.949   $73.95   $73.95   $73.90  
  7 purchase totals = $655.25       $716.0891   $716.10   $716.10   $716.00