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 $209.59   13.652%   $238.2032   $238.20   $238.20   $238.20  
  Purchase #2 $112.54   11.739%   $125.7511   $125.75   $125.75   $125.80  
  Purchase #3 $212.45   11.457%   $236.7904   $236.79   $236.80   $236.80  
  Purchase #4 $119.83   10.834%   $132.8124   $132.81   $132.80   $132.80  
  Purchase #5 $60.47   7.580%   $65.0536   $65.05   $65.05   $65.10  
  Purchase #6 $105.76   13.471%   $120.0069   $120.01   $120.00   $120.00  
  Purchase #7 $133.51   5.612%   $141.0026   $141.00   $141.00   $141.00  
  7 purchase totals = $954.15       $1,059.6202   $1,059.61   $1,059.60   $1,059.70