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 $157.83   11.686%   $176.274   $176.27   $176.25   $176.30  
  Purchase #2 $10.77   11.603%   $12.0196   $12.02   $12.00   $12.00  
  Purchase #3 $20.94   13.197%   $23.7035   $23.70   $23.70   $23.70  
  Purchase #4 $190.25   12.798%   $214.5982   $214.60   $214.60   $214.60  
  Purchase #5 $54.29   11.731%   $60.6588   $60.66   $60.65   $60.70  
  Purchase #6 $211.80   3.307%   $218.8042   $218.80   $218.80   $218.80  
  Purchase #7 $170.99   12.377%   $192.1534   $192.15   $192.15   $192.20  
  7 purchase totals = $816.87       $898.2117   $898.20   $898.15   $898.30