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	$93.94	7.680%	$101.1546	$101.15	$101.15	$101.20
Purchase #2	$219.59	8.598%	$238.4703	$238.47	$238.45	$238.50
Purchase #3	$90.48	7.265%	$97.0534	$97.05	$97.05	$97.10
Purchase #4	$116.61	10.434%	$128.7771	$128.78	$128.80	$128.80
Purchase #5	$88.77	12.700%	$100.0438	$100.04	$100.05	$100.00
Purchase #6	$51.42	7.545%	$55.2996	$55.30	$55.30	$55.30
Purchase #7	$166.64	5.769%	$176.2535	$176.25	$176.25	$176.30
7 purchase totals =	$827.45		$897.0523	$897.04	$897.05	$897.20