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	$66.95	12.153%	$75.0864	$75.09	$75.10	$75.10
Purchase #2	$100.83	7.847%	$108.7421	$108.74	$108.75	$108.70
Purchase #3	$53.63	10.717%	$59.3775	$59.38	$59.40	$59.40
Purchase #4	$31.61	11.707%	$35.3106	$35.31	$35.30	$35.30
Purchase #5	$238.82	6.525%	$254.403	$254.40	$254.40	$254.40
Purchase #6	$37.45	10.383%	$41.3384	$41.34	$41.35	$41.30
Purchase #7	$9.47	13.227%	$10.7226	$10.72	$10.70	$10.70
7 purchase totals =	$538.76		$584.9806	$584.98	$585.00	$584.90