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 $82.77   11.760%   $92.5038   $92.50   $92.50   $92.50  
  Purchase #2 $240.77   8.734%   $261.7989   $261.80   $261.80   $261.80  
  Purchase #3 $75.32   10.831%   $83.4779   $83.48   $83.50   $83.50  
  Purchase #4 $240.51   5.759%   $254.361   $254.36   $254.35   $254.40  
  Purchase #5 $230.93   4.825%   $242.0724   $242.07   $242.05   $242.10  
  Purchase #6 $114.30   9.210%   $124.827   $124.83   $124.85   $124.80  
  Purchase #7 $217.31   4.411%   $226.8955   $226.90   $226.90   $226.90  
  7 purchase totals = $1,201.91       $1,285.9365   $1,285.94   $1,285.95   $1,286.00