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 $211.25   10.721%   $233.8981   $233.90   $233.90   $233.90  
  Purchase #2 $181.82   9.807%   $199.6511   $199.65   $199.65   $199.70  
  Purchase #3 $176.86   8.522%   $191.932   $191.93   $191.95   $191.90  
  Purchase #4 $34.60   11.484%   $38.5735   $38.57   $38.55   $38.60  
  Purchase #5 $7.91   9.768%   $8.6826   $8.68   $8.70   $8.70  
  Purchase #6 $161.92   7.578%   $174.1903   $174.19   $174.20   $174.20  
  Purchase #7 $112.87   5.807%   $119.4244   $119.42   $119.40   $119.40  
  7 purchase totals = $887.23       $966.3520   $966.34   $966.35   $966.40