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 $235.37   11.555%   $262.567   $262.57   $262.55   $262.60  
  Purchase #2 $47.54   6.758%   $50.7528   $50.75   $50.75   $50.80  
  Purchase #3 $81.91   5.344%   $86.2873   $86.29   $86.30   $86.30  
  Purchase #4 $199.43   13.628%   $226.6083   $226.61   $226.60   $226.60  
  Purchase #5 $93.77   13.465%   $106.3961   $106.40   $106.40   $106.40  
  Purchase #6 $161.27   9.139%   $176.0085   $176.01   $176.00   $176.00  
  Purchase #7 $18.53   9.546%   $20.2989   $20.30   $20.30   $20.30  
  7 purchase totals = $837.82       $928.9189   $928.93   $928.90   $929.00