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 $63.28   6.763%   $67.5596   $67.56   $67.55   $67.60  
  Purchase #2 $184.80   11.667%   $206.3606   $206.36   $206.35   $206.40  
  Purchase #3 $19.32   6.634%   $20.6017   $20.60   $20.60   $20.60  
  Purchase #4 $227.61   8.639%   $247.2732   $247.27   $247.25   $247.30  
  Purchase #5 $20.89   9.149%   $22.8012   $22.80   $22.80   $22.80  
  Purchase #6 $92.73   6.570%   $98.8224   $98.82   $98.80   $98.80  
  Purchase #7 $197.76   9.844%   $217.2275   $217.23   $217.25   $217.20  
  7 purchase totals = $806.39       $880.6462   $880.64   $880.60   $880.70