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 $241.94   13.872%   $275.5019   $275.50   $275.50   $275.50  
  Purchase #2 $59.37   10.734%   $65.7428   $65.74   $65.75   $65.70  
  Purchase #3 $163.63   5.586%   $172.7704   $172.77   $172.75   $172.80  
  Purchase #4 $194.41   13.189%   $220.0507   $220.05   $220.05   $220.10  
  Purchase #5 $214.32   8.301%   $232.1107   $232.11   $232.10   $232.10  
  Purchase #6 $153.90   7.815%   $165.9273   $165.93   $165.95   $165.90  
  Purchase #7 $175.80   4.602%   $183.8903   $183.89   $183.90   $183.90  
  7 purchase totals = $1,203.37       $1,315.9941   $1,315.99   $1,316.00   $1,316.00