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 $233.96   11.812%   $261.5954   $261.60   $261.60   $261.60  
  Purchase #2 $113.57   11.720%   $126.8804   $126.88   $126.90   $126.90  
  Purchase #3 $204.42   4.406%   $213.4267   $213.43   $213.45   $213.40  
  Purchase #4 $39.75   8.811%   $43.2524   $43.25   $43.25   $43.30  
  Purchase #5 $244.49   6.577%   $260.5701   $260.57   $260.55   $260.60  
  Purchase #6 $215.71   12.568%   $242.8204   $242.82   $242.80   $242.80  
  Purchase #7 $38.31   12.127%   $42.9559   $42.96   $42.95   $43.00  
  7 purchase totals = $1,090.21       $1,191.5013   $1,191.51   $1,191.50   $1,191.60