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 $6.93   4.757%   $7.2597   $7.26   $7.25   $7.30  
  Purchase #2 $58.46   11.376%   $65.1104   $65.11   $65.10   $65.10  
  Purchase #3 $65.47   5.697%   $69.1998   $69.20   $69.20   $69.20  
  Purchase #4 $160.48   9.472%   $175.6807   $175.68   $175.70   $175.70  
  Purchase #5 $250.70   13.352%   $284.1735   $284.17   $284.15   $284.20  
  Purchase #6 $153.37   10.761%   $169.8741   $169.87   $169.85   $169.90  
  Purchase #7 $206.28   9.552%   $225.9839   $225.98   $226.00   $226.00  
  7 purchase totals = $901.69       $997.2821   $997.27   $997.25   $997.40