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 $66.55   10.519%   $73.5504   $73.55   $73.55   $73.60  
  Purchase #2 $32.70   8.117%   $35.3543   $35.35   $35.35   $35.40  
  Purchase #3 $215.97   8.280%   $233.8523   $233.85   $233.85   $233.90  
  Purchase #4 $49.88   4.791%   $52.2698   $52.27   $52.25   $52.30  
  Purchase #5 $195.96   9.616%   $214.8035   $214.80   $214.80   $214.80  
  Purchase #6 $161.35   3.104%   $166.3583   $166.36   $166.35   $166.40  
  Purchase #7 $42.87   10.231%   $47.256   $47.26   $47.25   $47.30  
  7 purchase totals = $765.28       $823.4446   $823.44   $823.40   $823.70