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 $47.91   12.132%   $53.7224   $53.72   $53.70   $53.70  
  Purchase #2 $109.98   13.808%   $125.166   $125.17   $125.15   $125.20  
  Purchase #3 $207.25   5.537%   $218.7254   $218.73   $218.75   $218.70  
  Purchase #4 $108.56   9.868%   $119.2727   $119.27   $119.25   $119.30  
  Purchase #5 $151.27   12.282%   $169.849   $169.85   $169.85   $169.80  
  Purchase #6 $191.64   7.570%   $206.1471   $206.15   $206.15   $206.10  
  Purchase #7 $117.90   12.502%   $132.6399   $132.64   $132.65   $132.60  
  7 purchase totals = $934.51       $1,025.5225   $1,025.53   $1,025.50   $1,025.40