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	$165.69	11.348%	$184.4925	$184.49	$184.50	$184.50
Purchase #2	$121.86	4.616%	$127.4851	$127.49	$127.50	$127.50
Purchase #3	$175.82	7.767%	$189.4759	$189.48	$189.50	$189.50
Purchase #4	$139.57	9.681%	$153.0818	$153.08	$153.10	$153.10
Purchase #5	$6.88	12.128%	$7.7144	$7.71	$7.70	$7.70
Purchase #6	$10.95	12.146%	$12.28	$12.28	$12.30	$12.30
Purchase #7	$94.83	10.813%	$105.084	$105.08	$105.10	$105.10
7 purchase totals =	$715.60		$779.6137	$779.61	$779.70	$779.70