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 $52.66   13.429%   $59.7317   $59.73   $59.75   $59.70  
  Purchase #2 $42.97   11.338%   $47.8419   $47.84   $47.85   $47.80  
  Purchase #3 $68.89   9.419%   $75.3787   $75.38   $75.40   $75.40  
  Purchase #4 $44.73   8.248%   $48.4193   $48.42   $48.40   $48.40  
  Purchase #5 $39.80   4.707%   $41.6734   $41.67   $41.65   $41.70  
  Purchase #6 $237.41   8.820%   $258.3496   $258.35   $258.35   $258.30  
  Purchase #7 $210.48   6.191%   $223.5108   $223.51   $223.50   $223.50  
  7 purchase totals = $696.94       $754.9054   $754.90   $754.90   $754.80