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 $235.48   13.803%   $267.9833   $267.98   $268.00   $268.00  
  Purchase #2 $51.64   12.333%   $58.0088   $58.01   $58.00   $58.00  
  Purchase #3 $77.62   13.811%   $88.3401   $88.34   $88.35   $88.30  
  Purchase #4 $122.38   9.788%   $134.3586   $134.36   $134.35   $134.40  
  Purchase #5 $49.49   10.346%   $54.6102   $54.61   $54.60   $54.60  
  Purchase #6 $119.63   13.487%   $135.7645   $135.76   $135.75   $135.80  
  Purchase #7 $246.61   6.297%   $262.139   $262.14   $262.15   $262.10  
  7 purchase totals = $902.85       $1,001.2045   $1,001.20   $1,001.20   $1,001.20