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 $59.71   12.815%   $67.3618   $67.36   $67.35   $67.40  
  Purchase #2 $235.37   3.762%   $244.2246   $244.22   $244.20   $244.20  
  Purchase #3 $49.50   4.498%   $51.7265   $51.73   $51.75   $51.70  
  Purchase #4 $125.33   3.659%   $129.9158   $129.92   $129.90   $129.90  
  Purchase #5 $95.73   13.769%   $108.9111   $108.91   $108.90   $108.90  
  Purchase #6 $132.95   6.658%   $141.8018   $141.80   $141.80   $141.80  
  Purchase #7 $103.82   10.315%   $114.529   $114.53   $114.55   $114.50  
  7 purchase totals = $802.41       $858.4706   $858.47   $858.45   $858.40