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 $240.96   5.832%   $255.0128   $255.01   $255.00   $255.00  
  Purchase #2 $113.32   11.118%   $125.9189   $125.92   $125.90   $125.90  
  Purchase #3 $227.71   6.691%   $242.9461   $242.95   $242.95   $242.90  
  Purchase #4 $71.37   9.825%   $78.3821   $78.38   $78.40   $78.40  
  Purchase #5 $129.42   5.122%   $136.0489   $136.05   $136.05   $136.00  
  Purchase #6 $103.84   10.457%   $114.6985   $114.70   $114.70   $114.70  
  Purchase #7 $212.77   4.251%   $221.8149   $221.81   $221.80   $221.80  
  7 purchase totals = $1,099.39       $1,174.8222   $1,174.82   $1,174.80   $1,174.70