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 $68.51   9.395%   $74.9465   $74.95   $74.95   $74.90  
  Purchase #2 $15.63   12.474%   $17.5797   $17.58   $17.60   $17.60  
  Purchase #3 $185.82   8.552%   $201.7113   $201.71   $201.70   $201.70  
  Purchase #4 $194.25   3.480%   $201.0099   $201.01   $201.00   $201.00  
  Purchase #5 $242.75   6.317%   $258.0845   $258.08   $258.10   $258.10  
  Purchase #6 $41.56   11.843%   $46.482   $46.48   $46.50   $46.50  
  Purchase #7 $90.75   11.480%   $101.1681   $101.17   $101.15   $101.20  
  7 purchase totals = $839.27       $900.9820   $900.98   $901.00   $901.00