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 $68.49   7.450%   $73.5925   $73.59   $73.60   $73.60  
  Purchase #2 $15.66   8.306%   $16.9607   $16.96   $16.95   $17.00  
  Purchase #3 $46.96   3.452%   $48.5811   $48.58   $48.60   $48.60  
  Purchase #4 $170.53   3.205%   $175.9955   $176.00   $176.00   $176.00  
  Purchase #5 $204.99   7.604%   $220.5774   $220.58   $220.60   $220.60  
  Purchase #6 $127.58   11.505%   $142.2581   $142.26   $142.25   $142.30  
  Purchase #7 $125.35   12.444%   $140.9486   $140.95   $140.95   $140.90  
  7 purchase totals = $759.56       $818.9139   $818.92   $818.95   $819.00