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 $39.53   10.180%   $43.5542   $43.55   $43.55   $43.60  
  Purchase #2 $218.92   10.482%   $241.8672   $241.87   $241.85   $241.90  
  Purchase #3 $195.69   6.136%   $207.6975   $207.70   $207.70   $207.70  
  Purchase #4 $49.33   3.853%   $51.2307   $51.23   $51.25   $51.20  
  Purchase #5 $61.89   5.541%   $65.3193   $65.32   $65.30   $65.30  
  Purchase #6 $250.59   4.831%   $262.696   $262.70   $262.70   $262.70  
  Purchase #7 $74.75   5.633%   $78.9607   $78.96   $78.95   $79.00  
  7 purchase totals = $890.70       $951.3256   $951.33   $951.30   $951.40