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 $10.45   11.787%   $11.6817   $11.68   $11.70   $11.70  
  Purchase #2 $111.43   7.386%   $119.6602   $119.66   $119.65   $119.70  
  Purchase #3 $87.29   6.213%   $92.7133   $92.71   $92.70   $92.70  
  Purchase #4 $59.73   13.110%   $67.5606   $67.56   $67.55   $67.60  
  Purchase #5 $45.38   13.129%   $51.3379   $51.34   $51.35   $51.30  
  Purchase #6 $234.78   13.610%   $266.7336   $266.73   $266.75   $266.70  
  Purchase #7 $128.41   9.494%   $140.6012   $140.60   $140.60   $140.60  
  7 purchase totals = $677.47       $750.2885   $750.28   $750.30   $750.30