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 $113.89   11.307%   $126.7675   $126.77   $126.75   $126.80  
  Purchase #2 $228.37   3.534%   $236.4406   $236.44   $236.45   $236.40  
  Purchase #3 $47.37   9.543%   $51.8905   $51.89   $51.90   $51.90  
  Purchase #4 $156.85   9.570%   $171.8605   $171.86   $171.85   $171.90  
  Purchase #5 $91.39   4.484%   $95.4879   $95.49   $95.50   $95.50  
  Purchase #6 $247.55   5.447%   $261.034   $261.03   $261.05   $261.00  
  Purchase #7 $5.30   13.343%   $6.0072   $6.01   $6.00   $6.00  
  7 purchase totals = $890.72       $949.4882   $949.49   $949.50   $949.50