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 $40.73   6.147%   $43.2337   $43.23   $43.25   $43.20  
  Purchase #2 $182.51   11.423%   $203.3581   $203.36   $203.35   $203.40  
  Purchase #3 $156.58   11.291%   $174.2594   $174.26   $174.25   $174.30  
  Purchase #4 $72.84   4.637%   $76.2176   $76.22   $76.20   $76.20  
  Purchase #5 $212.64   4.149%   $221.4624   $221.46   $221.45   $221.50  
  Purchase #6 $237.26   5.748%   $250.8977   $250.90   $250.90   $250.90  
  Purchase #7 $192.51   9.598%   $210.9871   $210.99   $211.00   $211.00  
  7 purchase totals = $1,095.07       $1,180.4160   $1,180.42   $1,180.40   $1,180.50