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 $85.43   12.537%   $96.1404   $96.14   $96.15   $96.10  
  Purchase #2 $169.52   7.342%   $181.9662   $181.97   $181.95   $182.00  
  Purchase #3 $123.25   3.480%   $127.5391   $127.54   $127.55   $127.50  
  Purchase #4 $118.47   5.665%   $125.1813   $125.18   $125.20   $125.20  
  Purchase #5 $66.91   7.205%   $71.7309   $71.73   $71.75   $71.70  
  Purchase #6 $92.43   13.518%   $104.9247   $104.92   $104.90   $104.90  
  Purchase #7 $53.99   11.165%   $60.018   $60.02   $60.00   $60.00  
  7 purchase totals = $710.00       $767.5006   $767.50   $767.50   $767.40