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 $239.29   6.692%   $255.3033   $255.30   $255.30   $255.30  
  Purchase #2 $210.62   13.296%   $238.624   $238.62   $238.60   $238.60  
  Purchase #3 $46.27   9.543%   $50.6855   $50.69   $50.70   $50.70  
  Purchase #4 $243.46   7.633%   $262.0433   $262.04   $262.05   $262.00  
  Purchase #5 $245.63   10.586%   $271.6324   $271.63   $271.65   $271.60  
  Purchase #6 $214.99   11.810%   $240.3803   $240.38   $240.40   $240.40  
  Purchase #7 $34.62   11.556%   $38.6207   $38.62   $38.60   $38.60  
  7 purchase totals = $1,234.88       $1,357.2895   $1,357.28   $1,357.30   $1,357.20