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 $48.94   11.614%   $54.6239   $54.62   $54.60   $54.60  
  Purchase #2 $102.66   8.118%   $110.9939   $110.99   $111.00   $111.00  
  Purchase #3 $121.44   6.725%   $129.6068   $129.61   $129.60   $129.60  
  Purchase #4 $41.94   13.768%   $47.7143   $47.71   $47.70   $47.70  
  Purchase #5 $203.97   3.505%   $211.1191   $211.12   $211.10   $211.10  
  Purchase #6 $227.83   5.105%   $239.4607   $239.46   $239.45   $239.50  
  Purchase #7 $148.37   3.478%   $153.5303   $153.53   $153.55   $153.50  
  7 purchase totals = $895.15       $947.0490   $947.04   $947.00   $947.00