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 $45.63   6.658%   $48.668   $48.67   $48.65   $48.70  
  Purchase #2 $31.88   12.548%   $35.8803   $35.88   $35.90   $35.90  
  Purchase #3 $112.54   5.281%   $118.4832   $118.48   $118.50   $118.50  
  Purchase #4 $155.90   5.647%   $164.7037   $164.70   $164.70   $164.70  
  Purchase #5 $236.88   11.702%   $264.5997   $264.60   $264.60   $264.60  
  Purchase #6 $65.45   13.591%   $74.3453   $74.35   $74.35   $74.30  
  Purchase #7 $236.42   8.692%   $256.9696   $256.97   $256.95   $257.00  
  7 purchase totals = $884.70       $963.6498   $963.65   $963.65   $963.70