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 $164.63   10.520%   $181.9491   $181.95   $181.95   $181.90  
  Purchase #2 $65.42   6.545%   $69.7017   $69.70   $69.70   $69.70  
  Purchase #3 $241.28   10.671%   $267.027   $267.03   $267.05   $267.00  
  Purchase #4 $137.62   11.582%   $153.5591   $153.56   $153.55   $153.60  
  Purchase #5 $129.38   3.388%   $133.7634   $133.76   $133.75   $133.80  
  Purchase #6 $35.36   12.845%   $39.902   $39.90   $39.90   $39.90  
  Purchase #7 $117.88   8.455%   $127.8468   $127.85   $127.85   $127.80  
  7 purchase totals = $891.57       $973.7491   $973.75   $973.75   $973.70