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 $131.66   13.318%   $149.1945   $149.19   $149.20   $149.20  
  Purchase #2 $75.71   8.190%   $81.9106   $81.91   $81.90   $81.90  
  Purchase #3 $226.84   13.256%   $256.9099   $256.91   $256.90   $256.90  
  Purchase #4 $60.70   7.430%   $65.21   $65.21   $65.20   $65.20  
  Purchase #5 $71.73   6.580%   $76.4498   $76.45   $76.45   $76.40  
  Purchase #6 $121.94   3.597%   $126.3262   $126.33   $126.35   $126.30  
  Purchase #7 $44.45   13.184%   $50.3103   $50.31   $50.30   $50.30  
  7 purchase totals = $733.03       $806.3113   $806.31   $806.30   $806.20