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 $47.96   11.391%   $53.4231   $53.42   $53.40   $53.40  
  Purchase #2 $145.51   7.195%   $155.9794   $155.98   $156.00   $156.00  
  Purchase #3 $97.32   12.871%   $109.8461   $109.85   $109.85   $109.80  
  Purchase #4 $104.67   7.350%   $112.3632   $112.36   $112.35   $112.40  
  Purchase #5 $64.54   13.444%   $73.2168   $73.22   $73.20   $73.20  
  Purchase #6 $58.72   12.387%   $65.9936   $65.99   $66.00   $66.00  
  Purchase #7 $213.50   9.610%   $234.0174   $234.02   $234.00   $234.00  
  7 purchase totals = $732.22       $804.8396   $804.84   $804.80   $804.80