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 $70.47   8.503%   $76.4621   $76.46   $76.45   $76.50  
  Purchase #2 $105.32   12.273%   $118.2459   $118.25   $118.25   $118.20  
  Purchase #3 $164.56   8.283%   $178.1905   $178.19   $178.20   $178.20  
  Purchase #4 $115.62   9.407%   $126.4964   $126.50   $126.50   $126.50  
  Purchase #5 $72.51   7.230%   $77.7525   $77.75   $77.75   $77.80  
  Purchase #6 $36.75   9.706%   $40.317   $40.32   $40.30   $40.30  
  Purchase #7 $137.88   8.165%   $149.1379   $149.14   $149.15   $149.10  
  7 purchase totals = $703.11       $766.6023   $766.61   $766.60   $766.60