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 $32.73   3.347%   $33.8255   $33.83   $33.85   $33.80  
  Purchase #2 $166.82   5.741%   $176.3971   $176.40   $176.40   $176.40  
  Purchase #3 $55.61   5.804%   $58.8376   $58.84   $58.85   $58.80  
  Purchase #4 $207.53   8.806%   $225.8051   $225.81   $225.80   $225.80  
  Purchase #5 $48.90   5.523%   $51.6007   $51.60   $51.60   $51.60  
  Purchase #6 $175.75   10.738%   $194.622   $194.62   $194.60   $194.60  
  Purchase #7 $208.83   11.834%   $233.5429   $233.54   $233.55   $233.50  
  7 purchase totals = $896.17       $974.6309   $974.64   $974.65   $974.50