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 $54.73   10.601%   $60.5319   $60.53   $60.55   $60.50  
  Purchase #2 $240.31   4.351%   $250.7659   $250.77   $250.75   $250.80  
  Purchase #3 $158.70   6.665%   $169.2774   $169.28   $169.30   $169.30  
  Purchase #4 $104.29   7.581%   $112.1962   $112.20   $112.20   $112.20  
  Purchase #5 $143.51   5.536%   $151.4547   $151.45   $151.45   $151.50  
  Purchase #6 $246.53   7.232%   $264.359   $264.36   $264.35   $264.40  
  Purchase #7 $14.63   7.302%   $15.6983   $15.70   $15.70   $15.70  
  7 purchase totals = $962.70       $1,024.2834   $1,024.29   $1,024.30   $1,024.40