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 $54.92   6.316%   $58.3887   $58.39   $58.40   $58.40  
  Purchase #2 $184.38   9.770%   $202.3939   $202.39   $202.40   $202.40  
  Purchase #3 $151.90   8.551%   $164.889   $164.89   $164.90   $164.90  
  Purchase #4 $244.72   6.589%   $260.8446   $260.84   $260.85   $260.80  
  Purchase #5 $218.50   8.392%   $236.8365   $236.84   $236.85   $236.80  
  Purchase #6 $247.60   5.542%   $261.322   $261.32   $261.30   $261.30  
  Purchase #7 $157.84   3.222%   $162.9256   $162.93   $162.95   $162.90  
  7 purchase totals = $1,259.86       $1,347.6003   $1,347.60   $1,347.65   $1,347.50