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 $56.79   7.377%   $60.9794   $60.98   $61.00   $61.00  
  Purchase #2 $105.86   12.154%   $118.7262   $118.73   $118.75   $118.70  
  Purchase #3 $247.48   10.713%   $273.9925   $273.99   $274.00   $274.00  
  Purchase #4 $215.94   10.115%   $237.7823   $237.78   $237.80   $237.80  
  Purchase #5 $15.63   10.228%   $17.2286   $17.23   $17.25   $17.20  
  Purchase #6 $240.39   5.214%   $252.9239   $252.92   $252.90   $252.90  
  Purchase #7 $33.76   4.161%   $35.1648   $35.16   $35.15   $35.20  
  7 purchase totals = $915.85       $996.7977   $996.79   $996.85   $996.80