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 $63.25   4.591%   $66.1538   $66.15   $66.15   $66.20  
  Purchase #2 $24.47   3.704%   $25.3764   $25.38   $25.40   $25.40  
  Purchase #3 $173.93   7.105%   $186.2877   $186.29   $186.30   $186.30  
  Purchase #4 $166.59   3.282%   $172.0575   $172.06   $172.05   $172.10  
  Purchase #5 $8.60   7.816%   $9.2722   $9.27   $9.25   $9.30  
  Purchase #6 $243.77   3.119%   $251.3732   $251.37   $251.35   $251.40  
  Purchase #7 $41.42   11.662%   $46.2504   $46.25   $46.25   $46.30  
  7 purchase totals = $722.03       $756.7712   $756.77   $756.75   $757.00