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 $10.68   9.292%   $11.6724   $11.67   $11.65   $11.70  
  Purchase #2 $155.34   13.487%   $176.2907   $176.29   $176.30   $176.30  
  Purchase #3 $182.94   13.550%   $207.7284   $207.73   $207.75   $207.70  
  Purchase #4 $25.71   6.833%   $27.4668   $27.47   $27.45   $27.50  
  Purchase #5 $163.40   5.592%   $172.5373   $172.54   $172.55   $172.50  
  Purchase #6 $146.54   10.614%   $162.0938   $162.09   $162.10   $162.10  
  Purchase #7 $174.70   7.164%   $187.2155   $187.22   $187.20   $187.20  
  7 purchase totals = $859.31       $945.0049   $945.01   $945.00   $945.00