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 $245.59   9.301%   $268.4323   $268.43   $268.45   $268.40  
  Purchase #2 $143.94   13.448%   $163.2971   $163.30   $163.30   $163.30  
  Purchase #3 $205.34   13.331%   $232.7139   $232.71   $232.70   $232.70  
  Purchase #4 $104.61   13.607%   $118.8443   $118.84   $118.85   $118.80  
  Purchase #5 $101.76   11.670%   $113.6354   $113.64   $113.65   $113.60  
  Purchase #6 $16.46   5.234%   $17.3215   $17.32   $17.30   $17.30  
  Purchase #7 $29.59   10.483%   $32.6919   $32.69   $32.70   $32.70  
  7 purchase totals = $847.29       $946.9364   $946.93   $946.95   $946.80