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 $188.93   9.443%   $206.7707   $206.77   $206.75   $206.80  
  Purchase #2 $64.80   4.559%   $67.7542   $67.75   $67.75   $67.80  
  Purchase #3 $232.44   6.475%   $247.4905   $247.49   $247.50   $247.50  
  Purchase #4 $162.94   7.804%   $175.6558   $175.66   $175.65   $175.70  
  Purchase #5 $70.43   7.610%   $75.7897   $75.79   $75.80   $75.80  
  Purchase #6 $233.63   5.571%   $246.6455   $246.65   $246.65   $246.60  
  Purchase #7 $243.76   7.282%   $261.5106   $261.51   $261.50   $261.50  
  7 purchase totals = $1,196.93       $1,281.6170   $1,281.62   $1,281.60   $1,281.70