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 $232.51   11.460%   $259.1556   $259.16   $259.15   $259.20  
  Purchase #2 $239.73   9.659%   $262.8855   $262.89   $262.90   $262.90  
  Purchase #3 $132.66   5.553%   $140.0266   $140.03   $140.05   $140.00  
  Purchase #4 $41.46   7.247%   $44.4646   $44.46   $44.45   $44.50  
  Purchase #5 $190.95   7.116%   $204.538   $204.54   $204.55   $204.50  
  Purchase #6 $218.34   3.169%   $225.2592   $225.26   $225.25   $225.30  
  Purchase #7 $225.52   13.447%   $255.8457   $255.85   $255.85   $255.80  
  7 purchase totals = $1,281.17       $1,392.1752   $1,392.19   $1,392.20   $1,392.20