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 $41.97   13.147%   $47.4878   $47.49   $47.50   $47.50  
  Purchase #2 $212.94   8.760%   $231.5935   $231.59   $231.60   $231.60  
  Purchase #3 $35.81   12.398%   $40.2497   $40.25   $40.25   $40.20  
  Purchase #4 $174.43   13.865%   $198.6147   $198.61   $198.60   $198.60  
  Purchase #5 $179.88   12.705%   $202.7338   $202.73   $202.75   $202.70  
  Purchase #6 $236.41   12.639%   $266.2899   $266.29   $266.30   $266.30  
  Purchase #7 $130.40   8.123%   $140.9924   $140.99   $141.00   $141.00  
  7 purchase totals = $1,011.84       $1,127.9618   $1,127.95   $1,128.00   $1,127.90