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 $213.85   13.134%   $241.9371   $241.94   $241.95   $241.90  
  Purchase #2 $42.44   6.772%   $45.314   $45.31   $45.30   $45.30  
  Purchase #3 $247.92   5.372%   $261.2383   $261.24   $261.25   $261.20  
  Purchase #4 $58.88   8.648%   $63.9719   $63.97   $63.95   $64.00  
  Purchase #5 $55.35   4.713%   $57.9586   $57.96   $57.95   $58.00  
  Purchase #6 $101.42   6.669%   $108.1837   $108.18   $108.20   $108.20  
  Purchase #7 $13.49   4.478%   $14.0941   $14.09   $14.10   $14.10  
  7 purchase totals = $733.35       $792.6977   $792.69   $792.70   $792.70