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 $71.97   6.776%   $76.8467   $76.85   $76.85   $76.80  
  Purchase #2 $62.59   13.792%   $71.2224   $71.22   $71.20   $71.20  
  Purchase #3 $124.86   11.567%   $139.3026   $139.30   $139.30   $139.30  
  Purchase #4 $141.92   4.624%   $148.4824   $148.48   $148.50   $148.50  
  Purchase #5 $158.83   13.240%   $179.8591   $179.86   $179.85   $179.90  
  Purchase #6 $220.59   10.610%   $243.9946   $243.99   $244.00   $244.00  
  Purchase #7 $168.73   4.281%   $175.9533   $175.95   $175.95   $176.00  
  7 purchase totals = $949.49       $1,035.6611   $1,035.65   $1,035.65   $1,035.70