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	$77.82	5.472%	$82.0783	$82.08	$82.10	$82.10
Purchase #2	$226.89	3.615%	$235.0921	$235.09	$235.10	$235.10
Purchase #3	$90.38	10.213%	$99.6105	$99.61	$99.60	$99.60
Purchase #4	$146.33	13.363%	$165.8841	$165.88	$165.90	$165.90
Purchase #5	$59.54	10.385%	$65.7232	$65.72	$65.70	$65.70
Purchase #6	$193.74	9.234%	$211.63	$211.63	$211.65	$211.60
Purchase #7	$233.91	8.872%	$254.6625	$254.66	$254.65	$254.70
7 purchase totals =	$1,028.61		$1,114.6807	$1,114.67	$1,114.70	$1,114.70