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 $87.58   6.760%   $93.5004   $93.50   $93.50   $93.50  
  Purchase #2 $82.66   11.181%   $91.9022   $91.90   $91.90   $91.90  
  Purchase #3 $41.99   8.162%   $45.4172   $45.42   $45.40   $45.40  
  Purchase #4 $42.40   13.279%   $48.0303   $48.03   $48.05   $48.00  
  Purchase #5 $60.44   6.766%   $64.5294   $64.53   $64.55   $64.50  
  Purchase #6 $249.29   5.427%   $262.819   $262.82   $262.80   $262.80  
  Purchase #7 $202.26   3.396%   $209.1287   $209.13   $209.15   $209.10  
  7 purchase totals = $766.62       $815.3272   $815.33   $815.35   $815.20