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 $60.54   4.536%   $63.2861   $63.29   $63.30   $63.30  
  Purchase #2 $232.26   13.731%   $264.1516   $264.15   $264.15   $264.20  
  Purchase #3 $108.50   13.697%   $123.3612   $123.36   $123.35   $123.40  
  Purchase #4 $144.53   10.294%   $159.4079   $159.41   $159.40   $159.40  
  Purchase #5 $206.33   4.288%   $215.1774   $215.18   $215.20   $215.20  
  Purchase #6 $50.38   9.569%   $55.2009   $55.20   $55.20   $55.20  
  Purchase #7 $43.61   11.136%   $48.4664   $48.47   $48.45   $48.50  
  7 purchase totals = $846.15       $929.0515   $929.06   $929.05   $929.20