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 $224.86   11.459%   $250.6267   $250.63   $250.65   $250.60  
  Purchase #2 $200.57   7.219%   $215.0491   $215.05   $215.05   $215.00  
  Purchase #3 $144.62   7.667%   $155.708   $155.71   $155.70   $155.70  
  Purchase #4 $75.67   9.580%   $82.9192   $82.92   $82.90   $82.90  
  Purchase #5 $110.99   13.787%   $126.2922   $126.29   $126.30   $126.30  
  Purchase #6 $28.74   13.330%   $32.571   $32.57   $32.55   $32.60  
  Purchase #7 $87.49   4.747%   $91.6432   $91.64   $91.65   $91.60  
  7 purchase totals = $872.94       $954.8094   $954.81   $954.80   $954.70