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 $123.85   3.733%   $128.4733   $128.47   $128.45   $128.50  
  Purchase #2 $199.82   3.451%   $206.7158   $206.72   $206.70   $206.70  
  Purchase #3 $226.73   4.674%   $237.3274   $237.33   $237.35   $237.30  
  Purchase #4 $83.84   10.641%   $92.7614   $92.76   $92.75   $92.80  
  Purchase #5 $54.66   13.119%   $61.8308   $61.83   $61.85   $61.80  
  Purchase #6 $162.48   5.855%   $171.9932   $171.99   $172.00   $172.00  
  Purchase #7 $110.91   4.164%   $115.5283   $115.53   $115.55   $115.50  
  7 purchase totals = $962.29       $1,014.6302   $1,014.63   $1,014.65   $1,014.60