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 $197.26   3.186%   $203.5447   $203.54   $203.55   $203.50  
  Purchase #2 $81.72   13.351%   $92.6304   $92.63   $92.65   $92.60  
  Purchase #3 $57.41   13.138%   $64.9525   $64.95   $64.95   $65.00  
  Purchase #4 $34.60   8.197%   $37.4362   $37.44   $37.45   $37.40  
  Purchase #5 $137.28   5.136%   $144.3307   $144.33   $144.35   $144.30  
  Purchase #6 $46.29   7.228%   $49.6358   $49.64   $49.65   $49.60  
  Purchase #7 $180.66   3.663%   $187.2776   $187.28   $187.30   $187.30  
  7 purchase totals = $735.22       $779.8079   $779.81   $779.90   $779.70