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 $209.63   9.324%   $229.1759   $229.18   $229.20   $229.20  
  Purchase #2 $104.60   11.237%   $116.3539   $116.35   $116.35   $116.40  
  Purchase #3 $59.33   11.270%   $66.0165   $66.02   $66.00   $66.00  
  Purchase #4 $166.98   12.699%   $188.1848   $188.18   $188.20   $188.20  
  Purchase #5 $47.31   12.607%   $53.2744   $53.27   $53.25   $53.30  
  Purchase #6 $201.88   5.708%   $213.4033   $213.40   $213.40   $213.40  
  Purchase #7 $183.68   12.595%   $206.8145   $206.81   $206.80   $206.80  
  7 purchase totals = $973.41       $1,073.2233   $1,073.21   $1,073.20   $1,073.30