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 $45.97   11.697%   $51.3471   $51.35   $51.35   $51.30  
  Purchase #2 $206.67   3.726%   $214.3705   $214.37   $214.35   $214.40  
  Purchase #3 $53.68   7.810%   $57.8724   $57.87   $57.85   $57.90  
  Purchase #4 $185.38   11.425%   $206.5597   $206.56   $206.55   $206.60  
  Purchase #5 $95.45   9.857%   $104.8585   $104.86   $104.85   $104.90  
  Purchase #6 $98.28   10.500%   $108.5994   $108.60   $108.60   $108.60  
  Purchase #7 $197.88   3.464%   $204.7346   $204.73   $204.75   $204.70  
  7 purchase totals = $883.31       $948.3422   $948.34   $948.30   $948.40