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 $241.54   11.615%   $269.5949   $269.59   $269.60   $269.60  
  Purchase #2 $50.36   10.667%   $55.7319   $55.73   $55.75   $55.70  
  Purchase #3 $180.30   10.529%   $199.2838   $199.28   $199.30   $199.30  
  Purchase #4 $186.32   6.594%   $198.6059   $198.61   $198.60   $198.60  
  Purchase #5 $23.56   12.597%   $26.5279   $26.53   $26.55   $26.50  
  Purchase #6 $14.32   4.516%   $14.9667   $14.97   $14.95   $15.00  
  Purchase #7 $155.91   11.276%   $173.4904   $173.49   $173.50   $173.50  
  7 purchase totals = $852.31       $938.2015   $938.20   $938.25   $938.20