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	$180.51	4.856%	$189.2756	$189.28	$189.30	$189.30
Purchase #2	$158.88	4.676%	$166.3092	$166.31	$166.30	$166.30
Purchase #3	$170.65	9.471%	$186.8123	$186.81	$186.80	$186.80
Purchase #4	$49.76	9.438%	$54.4563	$54.46	$54.45	$54.50
Purchase #5	$56.35	12.655%	$63.4811	$63.48	$63.50	$63.50
Purchase #6	$57.50	13.613%	$65.3275	$65.33	$65.35	$65.30
Purchase #7	$47.80	5.680%	$50.515	$50.52	$50.50	$50.50
7 purchase totals =	$721.45		$776.1770	$776.19	$776.20	$776.20