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 $94.65   4.204%   $98.6291   $98.63   $98.65   $98.60  
  Purchase #2 $145.36   11.122%   $161.5269   $161.53   $161.55   $161.50  
  Purchase #3 $188.63   3.604%   $195.4282   $195.43   $195.45   $195.40  
  Purchase #4 $119.53   6.202%   $126.9433   $126.94   $126.95   $126.90  
  Purchase #5 $237.79   7.395%   $255.3746   $255.37   $255.35   $255.40  
  Purchase #6 $114.59   11.253%   $127.4848   $127.48   $127.50   $127.50  
  Purchase #7 $246.42   4.540%   $257.6075   $257.61   $257.60   $257.60  
  7 purchase totals = $1,146.97       $1,222.9944   $1,222.99   $1,223.05   $1,222.90