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 $43.84   10.102%   $48.2687   $48.27   $48.25   $48.30  
  Purchase #2 $115.44   5.707%   $122.0282   $122.03   $122.05   $122.00  
  Purchase #3 $116.90   11.490%   $130.3318   $130.33   $130.35   $130.30  
  Purchase #4 $164.49   9.870%   $180.7252   $180.73   $180.75   $180.70  
  Purchase #5 $215.71   11.419%   $240.3419   $240.34   $240.35   $240.30  
  Purchase #6 $55.42   6.459%   $58.9996   $59.00   $59.00   $59.00  
  Purchase #7 $107.68   13.635%   $122.3622   $122.36   $122.35   $122.40  
  7 purchase totals = $819.48       $903.0576   $903.06   $903.10   $903.00