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 $104.79   11.122%   $116.4447   $116.44   $116.45   $116.40  
  Purchase #2 $75.35   9.395%   $82.4291   $82.43   $82.45   $82.40  
  Purchase #3 $122.50   7.612%   $131.8247   $131.82   $131.80   $131.80  
  Purchase #4 $80.82   4.266%   $84.2678   $84.27   $84.25   $84.30  
  Purchase #5 $131.87   13.364%   $149.4931   $149.49   $149.50   $149.50  
  Purchase #6 $223.87   13.577%   $254.2648   $254.26   $254.25   $254.30  
  Purchase #7 $46.86   3.555%   $48.5259   $48.53   $48.55   $48.50  
  7 purchase totals = $786.06       $867.2501   $867.24   $867.25   $867.20