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 $174.59   12.761%   $196.8694   $196.87   $196.85   $196.90  
  Purchase #2 $110.62   7.247%   $118.6366   $118.64   $118.65   $118.60  
  Purchase #3 $23.99   8.419%   $26.0097   $26.01   $26.00   $26.00  
  Purchase #4 $239.61   8.806%   $260.7101   $260.71   $260.70   $260.70  
  Purchase #5 $227.89   9.158%   $248.7602   $248.76   $248.75   $248.80  
  Purchase #6 $242.96   4.355%   $253.5409   $253.54   $253.55   $253.50  
  Purchase #7 $228.38   4.695%   $239.1024   $239.10   $239.10   $239.10  
  7 purchase totals = $1,248.04       $1,343.6293   $1,343.63   $1,343.60   $1,343.60