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 $244.87   10.424%   $270.3952   $270.40   $270.40   $270.40  
  Purchase #2 $129.83   9.282%   $141.8808   $141.88   $141.90   $141.90  
  Purchase #3 $248.68   9.620%   $272.603   $272.60   $272.60   $272.60  
  Purchase #4 $206.79   5.788%   $218.759   $218.76   $218.75   $218.80  
  Purchase #5 $41.46   9.210%   $45.2785   $45.28   $45.30   $45.30  
  Purchase #6 $245.92   8.277%   $266.2748   $266.27   $266.25   $266.30  
  Purchase #7 $230.46   7.652%   $248.0948   $248.09   $248.10   $248.10  
  7 purchase totals = $1,348.01       $1,463.2861   $1,463.28   $1,463.30   $1,463.40