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 $116.44   9.296%   $127.2643   $127.26   $127.25   $127.30  
  Purchase #2 $107.46   13.165%   $121.6071   $121.61   $121.60   $121.60  
  Purchase #3 $24.45   8.414%   $26.5072   $26.51   $26.50   $26.50  
  Purchase #4 $74.93   10.729%   $82.9692   $82.97   $82.95   $83.00  
  Purchase #5 $72.75   4.437%   $75.9779   $75.98   $76.00   $76.00  
  Purchase #6 $124.28   10.370%   $137.1678   $137.17   $137.15   $137.20  
  Purchase #7 $51.54   4.641%   $53.932   $53.93   $53.95   $53.90  
  7 purchase totals = $571.85       $625.4255   $625.43   $625.40   $625.50