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 $104.97   7.817%   $113.1755   $113.18   $113.20   $113.20  
  Purchase #2 $126.84   9.815%   $139.2893   $139.29   $139.30   $139.30  
  Purchase #3 $68.81   10.227%   $75.8472   $75.85   $75.85   $75.80  
  Purchase #4 $61.70   12.703%   $69.5378   $69.54   $69.55   $69.50  
  Purchase #5 $83.61   12.232%   $93.8372   $93.84   $93.85   $93.80  
  Purchase #6 $34.70   11.547%   $38.7068   $38.71   $38.70   $38.70  
  Purchase #7 $216.30   10.346%   $238.6784   $238.68   $238.70   $238.70  
  7 purchase totals = $696.93       $769.0722   $769.09   $769.15   $769.00