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 $249.28   10.660%   $275.8532   $275.85   $275.85   $275.90  
  Purchase #2 $236.34   9.433%   $258.634   $258.63   $258.65   $258.60  
  Purchase #3 $151.72   12.808%   $171.1523   $171.15   $171.15   $171.20  
  Purchase #4 $69.90   5.133%   $73.488   $73.49   $73.50   $73.50  
  Purchase #5 $150.80   5.683%   $159.37   $159.37   $159.35   $159.40  
  Purchase #6 $67.46   11.314%   $75.0924   $75.09   $75.10   $75.10  
  Purchase #7 $187.82   3.281%   $193.9824   $193.98   $194.00   $194.00  
  7 purchase totals = $1,113.32       $1,207.5723   $1,207.56   $1,207.60   $1,207.70