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 $156.76   12.401%   $176.1998   $176.20   $176.20   $176.20  
  Purchase #2 $161.32   13.617%   $183.2869   $183.29   $183.30   $183.30  
  Purchase #3 $199.53   7.717%   $214.9277   $214.93   $214.95   $214.90  
  Purchase #4 $155.44   11.548%   $173.3902   $173.39   $173.40   $173.40  
  Purchase #5 $31.41   10.595%   $34.7379   $34.74   $34.75   $34.70  
  Purchase #6 $87.66   9.833%   $96.2796   $96.28   $96.30   $96.30  
  Purchase #7 $199.79   8.255%   $216.2827   $216.28   $216.30   $216.30  
  7 purchase totals = $991.91       $1,095.1048   $1,095.11   $1,095.20   $1,095.10