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 $10.76   10.761%   $11.9179   $11.92   $11.90   $11.90  
  Purchase #2 $242.33   7.539%   $260.5993   $260.60   $260.60   $260.60  
  Purchase #3 $154.55   10.472%   $170.7345   $170.73   $170.75   $170.70  
  Purchase #4 $145.43   12.345%   $163.3833   $163.38   $163.40   $163.40  
  Purchase #5 $72.90   4.561%   $76.225   $76.23   $76.25   $76.20  
  Purchase #6 $243.70   6.466%   $259.4576   $259.46   $259.45   $259.50  
  Purchase #7 $13.29   11.625%   $14.835   $14.84   $14.85   $14.80  
  7 purchase totals = $882.96       $957.1526   $957.16   $957.20   $957.10