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 $124.33   13.733%   $141.4042   $141.40   $141.40   $141.40  
  Purchase #2 $248.54   13.462%   $281.9985   $282.00   $282.00   $282.00  
  Purchase #3 $88.27   10.697%   $97.7122   $97.71   $97.70   $97.70  
  Purchase #4 $137.31   5.652%   $145.0708   $145.07   $145.05   $145.10  
  Purchase #5 $8.35   4.181%   $8.6991   $8.70   $8.70   $8.70  
  Purchase #6 $62.90   3.833%   $65.311   $65.31   $65.30   $65.30  
  Purchase #7 $180.69   11.490%   $201.4513   $201.45   $201.45   $201.50  
  7 purchase totals = $850.39       $941.6471   $941.64   $941.60   $941.70