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	$71.86	7.345%	$77.1381	$77.14	$77.15	$77.10
Purchase #2	$56.91	10.585%	$62.9339	$62.93	$62.95	$62.90
Purchase #3	$27.40	3.568%	$28.3776	$28.38	$28.40	$28.40
Purchase #4	$87.37	12.610%	$98.3874	$98.39	$98.40	$98.40
Purchase #5	$139.87	11.314%	$155.6949	$155.69	$155.70	$155.70
Purchase #6	$39.69	9.224%	$43.351	$43.35	$43.35	$43.40
Purchase #7	$40.42	4.285%	$42.152	$42.15	$42.15	$42.20
7 purchase totals =	$463.52		$508.0349	$508.03	$508.10	$508.10