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 $66.58   10.518%   $73.5829   $73.58   $73.60   $73.60  
  Purchase #2 $221.92   6.790%   $236.9884   $236.99   $237.00   $237.00  
  Purchase #3 $223.28   5.498%   $235.5559   $235.56   $235.55   $235.60  
  Purchase #4 $32.62   13.162%   $36.9134   $36.91   $36.90   $36.90  
  Purchase #5 $111.56   12.752%   $125.7861   $125.79   $125.80   $125.80  
  Purchase #6 $47.32   5.187%   $49.7745   $49.77   $49.75   $49.80  
  Purchase #7 $6.99   5.663%   $7.3858   $7.39   $7.40   $7.40  
  7 purchase totals = $710.27       $765.9870   $765.99   $766.00   $766.10