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 $44.43   10.662%   $49.1671   $49.17   $49.15   $49.20  
  Purchase #2 $183.66   8.871%   $199.9525   $199.95   $199.95   $200.00  
  Purchase #3 $41.82   13.820%   $47.5995   $47.60   $47.60   $47.60  
  Purchase #4 $237.65   8.221%   $257.1872   $257.19   $257.20   $257.20  
  Purchase #5 $183.70   5.413%   $193.6437   $193.64   $193.65   $193.60  
  Purchase #6 $129.65   5.419%   $136.6757   $136.68   $136.70   $136.70  
  Purchase #7 $176.67   11.473%   $196.9393   $196.94   $196.95   $196.90  
  7 purchase totals = $997.58       $1,081.1650   $1,081.17   $1,081.20   $1,081.20