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 $168.29   13.836%   $191.5746   $191.57   $191.55   $191.60  
  Purchase #2 $110.79   4.112%   $115.3457   $115.35   $115.35   $115.30  
  Purchase #3 $61.39   10.840%   $68.0447   $68.04   $68.05   $68.00  
  Purchase #4 $126.67   8.537%   $137.4838   $137.48   $137.50   $137.50  
  Purchase #5 $105.46   6.568%   $112.3866   $112.39   $112.40   $112.40  
  Purchase #6 $202.55   3.143%   $208.9161   $208.92   $208.90   $208.90  
  Purchase #7 $102.53   8.524%   $111.2697   $111.27   $111.25   $111.30  
  7 purchase totals = $877.68       $945.0212   $945.02   $945.00   $945.00