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 $224.62   10.732%   $248.7262   $248.73   $248.75   $248.70  
  Purchase #2 $197.87   3.491%   $204.7776   $204.78   $204.80   $204.80  
  Purchase #3 $48.70   4.590%   $50.9353   $50.94   $50.95   $50.90  
  Purchase #4 $228.37   3.191%   $235.6573   $235.66   $235.65   $235.70  
  Purchase #5 $157.79   13.259%   $178.7114   $178.71   $178.70   $178.70  
  Purchase #6 $224.63   4.359%   $234.4216   $234.42   $234.40   $234.40  
  Purchase #7 $221.93   3.745%   $230.2413   $230.24   $230.25   $230.20  
  7 purchase totals = $1,303.91       $1,383.4707   $1,383.48   $1,383.50   $1,383.40