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 $189.51   3.697%   $196.5162   $196.52   $196.50   $196.50  
  Purchase #2 $61.39   4.678%   $64.2618   $64.26   $64.25   $64.30  
  Purchase #3 $23.83   4.755%   $24.9631   $24.96   $24.95   $25.00  
  Purchase #4 $63.34   10.380%   $69.9147   $69.91   $69.90   $69.90  
  Purchase #5 $101.26   6.120%   $107.4571   $107.46   $107.45   $107.50  
  Purchase #6 $122.55   8.839%   $133.3822   $133.38   $133.40   $133.40  
  Purchase #7 $208.42   9.134%   $227.4571   $227.46   $227.45   $227.50  
  7 purchase totals = $770.30       $823.9522   $823.95   $823.90   $824.10