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 $56.73   11.343%   $63.1649   $63.16   $63.15   $63.20  
  Purchase #2 $75.28   5.648%   $79.5318   $79.53   $79.55   $79.50  
  Purchase #3 $87.78   6.384%   $93.3839   $93.38   $93.40   $93.40  
  Purchase #4 $23.42   6.141%   $24.8582   $24.86   $24.85   $24.90  
  Purchase #5 $24.82   11.484%   $27.6703   $27.67   $27.65   $27.70  
  Purchase #6 $197.45   5.598%   $208.5033   $208.50   $208.50   $208.50  
  Purchase #7 $231.54   6.549%   $246.7036   $246.70   $246.70   $246.70  
  7 purchase totals = $697.02       $743.8160   $743.80   $743.80   $743.90