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 $48.39   11.139%   $53.7802   $53.78   $53.80   $53.80  
  Purchase #2 $226.67   10.526%   $250.5293   $250.53   $250.55   $250.50  
  Purchase #3 $15.39   12.533%   $17.3188   $17.32   $17.30   $17.30  
  Purchase #4 $119.77   10.228%   $132.0201   $132.02   $132.00   $132.00  
  Purchase #5 $169.49   13.835%   $192.9389   $192.94   $192.95   $192.90  
  Purchase #6 $199.93   7.733%   $215.3906   $215.39   $215.40   $215.40  
  Purchase #7 $44.49   10.676%   $49.2398   $49.24   $49.25   $49.20  
  7 purchase totals = $824.13       $911.2177   $911.22   $911.25   $911.10