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 $173.97   12.522%   $195.7545   $195.75   $195.75   $195.80  
  Purchase #2 $23.74   4.291%   $24.7587   $24.76   $24.75   $24.80  
  Purchase #3 $80.76   10.732%   $89.4272   $89.43   $89.45   $89.40  
  Purchase #4 $15.96   8.652%   $17.3409   $17.34   $17.35   $17.30  
  Purchase #5 $167.93   10.690%   $185.8817   $185.88   $185.90   $185.90  
  Purchase #6 $151.70   8.581%   $164.7174   $164.72   $164.70   $164.70  
  Purchase #7 $178.89   9.409%   $195.7218   $195.72   $195.70   $195.70  
  7 purchase totals = $792.95       $873.6022   $873.60   $873.60   $873.60