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 $46.79   6.206%   $49.6938   $49.69   $49.70   $49.70  
  Purchase #2 $104.86   11.716%   $117.1454   $117.15   $117.15   $117.10  
  Purchase #3 $189.30   5.478%   $199.6699   $199.67   $199.65   $199.70  
  Purchase #4 $107.49   7.719%   $115.7872   $115.79   $115.80   $115.80  
  Purchase #5 $23.98   10.771%   $26.5629   $26.56   $26.55   $26.60  
  Purchase #6 $213.78   7.517%   $229.8498   $229.85   $229.85   $229.80  
  Purchase #7 $229.39   6.874%   $245.1583   $245.16   $245.15   $245.20  
  7 purchase totals = $915.59       $983.8673   $983.87   $983.85   $983.90