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 $188.74   8.595%   $204.9622   $204.96   $204.95   $205.00  
  Purchase #2 $34.33   11.342%   $38.2237   $38.22   $38.20   $38.20  
  Purchase #3 $164.64   9.569%   $180.3944   $180.39   $180.40   $180.40  
  Purchase #4 $234.26   5.574%   $247.3177   $247.32   $247.30   $247.30  
  Purchase #5 $239.57   9.365%   $262.0057   $262.01   $262.00   $262.00  
  Purchase #6 $75.90   9.130%   $82.8297   $82.83   $82.85   $82.80  
  Purchase #7 $192.82   4.836%   $202.1448   $202.14   $202.15   $202.10  
  7 purchase totals = $1,130.26       $1,217.8782   $1,217.87   $1,217.85   $1,217.80