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 $40.79   9.182%   $44.5353   $44.54   $44.55   $44.50  
  Purchase #2 $166.64   10.390%   $183.9539   $183.95   $183.95   $184.00  
  Purchase #3 $56.33   10.806%   $62.417   $62.42   $62.40   $62.40  
  Purchase #4 $180.93   6.470%   $192.6362   $192.64   $192.65   $192.60  
  Purchase #5 $115.72   7.478%   $124.3735   $124.37   $124.35   $124.40  
  Purchase #6 $196.83   8.684%   $213.9227   $213.92   $213.90   $213.90  
  Purchase #7 $34.29   10.106%   $37.7553   $37.76   $37.75   $37.80  
  7 purchase totals = $791.53       $859.5939   $859.60   $859.55   $859.60