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 $92.85   12.235%   $104.2102   $104.21   $104.20   $104.20  
  Purchase #2 $139.43   10.134%   $153.5598   $153.56   $153.55   $153.60  
  Purchase #3 $27.48   4.110%   $28.6094   $28.61   $28.60   $28.60  
  Purchase #4 $202.98   11.312%   $225.9411   $225.94   $225.95   $225.90  
  Purchase #5 $84.44   10.613%   $93.4016   $93.40   $93.40   $93.40  
  Purchase #6 $136.68   5.379%   $144.032   $144.03   $144.05   $144.00  
  Purchase #7 $164.81   10.406%   $181.9601   $181.96   $181.95   $182.00  
  7 purchase totals = $848.67       $931.7142   $931.71   $931.70   $931.70