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 $208.84   11.381%   $232.6081   $232.61   $232.60   $232.60  
  Purchase #2 $126.26   8.304%   $136.7446   $136.74   $136.75   $136.70  
  Purchase #3 $156.89   8.400%   $170.0688   $170.07   $170.05   $170.10  
  Purchase #4 $86.87   5.576%   $91.7139   $91.71   $91.70   $91.70  
  Purchase #5 $125.79   4.748%   $131.7625   $131.76   $131.75   $131.80  
  Purchase #6 $129.57   5.365%   $136.5214   $136.52   $136.50   $136.50  
  Purchase #7 $98.74   6.167%   $104.8293   $104.83   $104.85   $104.80  
  7 purchase totals = $932.96       $1,004.2486   $1,004.24   $1,004.20   $1,004.20