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 $206.65   5.562%   $218.1439   $218.14   $218.15   $218.10  
  Purchase #2 $186.71   4.255%   $194.6545   $194.65   $194.65   $194.70  
  Purchase #3 $114.84   3.634%   $119.0133   $119.01   $119.00   $119.00  
  Purchase #4 $47.32   3.862%   $49.1475   $49.15   $49.15   $49.10  
  Purchase #5 $7.40   12.195%   $8.3024   $8.30   $8.30   $8.30  
  Purchase #6 $175.74   10.763%   $194.6549   $194.65   $194.65   $194.70  
  Purchase #7 $231.74   12.248%   $260.1235   $260.12   $260.10   $260.10  
  7 purchase totals = $970.40       $1,044.0400   $1,044.02   $1,044.00   $1,044.00