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 $187.84   8.707%   $204.1952   $204.20   $204.20   $204.20  
  Purchase #2 $126.87   10.544%   $140.2472   $140.25   $140.25   $140.20  
  Purchase #3 $147.97   10.639%   $163.7125   $163.71   $163.70   $163.70  
  Purchase #4 $122.31   12.305%   $137.3602   $137.36   $137.35   $137.40  
  Purchase #5 $208.40   13.202%   $235.913   $235.91   $235.90   $235.90  
  Purchase #6 $135.42   8.186%   $146.5055   $146.51   $146.50   $146.50  
  Purchase #7 $44.94   4.233%   $46.8423   $46.84   $46.85   $46.80  
  7 purchase totals = $973.75       $1,074.7759   $1,074.78   $1,074.75   $1,074.70