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 $34.82   4.337%   $36.3301   $36.33   $36.35   $36.30  
  Purchase #2 $146.29   10.651%   $161.8713   $161.87   $161.85   $161.90  
  Purchase #3 $12.40   6.664%   $13.2263   $13.23   $13.25   $13.20  
  Purchase #4 $182.44   4.359%   $190.3926   $190.39   $190.40   $190.40  
  Purchase #5 $226.73   4.111%   $236.0509   $236.05   $236.05   $236.10  
  Purchase #6 $83.49   3.646%   $86.534   $86.53   $86.55   $86.50  
  Purchase #7 $245.61   11.403%   $273.6169   $273.62   $273.60   $273.60  
  7 purchase totals = $931.78       $998.0221   $998.02   $998.05   $998.00