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 $57.56   10.249%   $63.4593   $63.46   $63.45   $63.50  
  Purchase #2 $73.96   5.861%   $78.2948   $78.29   $78.30   $78.30  
  Purchase #3 $159.69   10.162%   $175.9177   $175.92   $175.90   $175.90  
  Purchase #4 $232.32   4.655%   $243.1345   $243.13   $243.15   $243.10  
  Purchase #5 $118.51   11.388%   $132.0059   $132.01   $132.00   $132.00  
  Purchase #6 $13.26   9.710%   $14.5475   $14.55   $14.55   $14.50  
  Purchase #7 $246.69   6.532%   $262.8038   $262.80   $262.80   $262.80  
  7 purchase totals = $901.99       $970.1635   $970.16   $970.15   $970.10