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 $66.95   9.826%   $73.5285   $73.53   $73.55   $73.50  
  Purchase #2 $201.96   10.375%   $222.9134   $222.91   $222.90   $222.90  
  Purchase #3 $90.77   11.420%   $101.1359   $101.14   $101.15   $101.10  
  Purchase #4 $60.86   5.653%   $64.3004   $64.30   $64.30   $64.30  
  Purchase #5 $156.44   8.702%   $170.0534   $170.05   $170.05   $170.10  
  Purchase #6 $173.81   13.125%   $196.6226   $196.62   $196.60   $196.60  
  Purchase #7 $18.36   4.666%   $19.2167   $19.22   $19.20   $19.20  
  7 purchase totals = $769.15       $847.7709   $847.77   $847.75   $847.70