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	$165.52	13.812%	$188.3816	$188.38	$188.40	$188.40
Purchase #2	$136.70	12.796%	$154.1921	$154.19	$154.20	$154.20
Purchase #3	$65.86	8.449%	$71.4245	$71.42	$71.40	$71.40
Purchase #4	$72.68	13.461%	$82.4635	$82.46	$82.45	$82.50
Purchase #5	$162.94	6.464%	$173.4724	$173.47	$173.45	$173.50
Purchase #6	$53.43	13.843%	$60.8263	$60.83	$60.85	$60.80
Purchase #7	$61.59	6.751%	$65.7479	$65.75	$65.75	$65.70
7 purchase totals =	$718.72		$796.5083	$796.50	$796.50	$796.50