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 $61.87   9.296%   $67.6214   $67.62   $67.60   $67.60  
  Purchase #2 $169.37   4.702%   $177.3338   $177.33   $177.35   $177.30  
  Purchase #3 $97.35   12.162%   $109.1897   $109.19   $109.20   $109.20  
  Purchase #4 $139.95   3.457%   $144.7881   $144.79   $144.80   $144.80  
  Purchase #5 $242.65   7.362%   $260.5139   $260.51   $260.50   $260.50  
  Purchase #6 $68.40   8.397%   $74.1435   $74.14   $74.15   $74.10  
  Purchase #7 $109.36   8.632%   $118.8   $118.80   $118.80   $118.80  
  7 purchase totals = $888.95       $952.3904   $952.38   $952.40   $952.30