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 $40.53   10.148%   $44.643   $44.64   $44.65   $44.60  
  Purchase #2 $119.76   4.315%   $124.9276   $124.93   $124.95   $124.90  
  Purchase #3 $194.65   7.425%   $209.1028   $209.10   $209.10   $209.10  
  Purchase #4 $233.30   12.346%   $262.1032   $262.10   $262.10   $262.10  
  Purchase #5 $40.42   7.670%   $43.5202   $43.52   $43.50   $43.50  
  Purchase #6 $166.93   11.116%   $185.4859   $185.49   $185.50   $185.50  
  Purchase #7 $32.60   5.136%   $34.2743   $34.27   $34.25   $34.30  
  7 purchase totals = $828.19       $904.0570   $904.05   $904.05   $904.00