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	$222.92	12.741%	$251.3222	$251.32	$251.30	$251.30
Purchase #2	$96.31	7.227%	$103.2703	$103.27	$103.25	$103.30
Purchase #3	$240.38	11.301%	$267.5453	$267.55	$267.55	$267.50
Purchase #4	$181.40	5.374%	$191.1484	$191.15	$191.15	$191.10
Purchase #5	$59.98	4.327%	$62.5753	$62.58	$62.60	$62.60
Purchase #6	$134.46	8.371%	$145.7156	$145.72	$145.70	$145.70
Purchase #7	$35.25	11.559%	$39.3245	$39.32	$39.30	$39.30
7 purchase totals =	$970.70		$1,060.9016	$1,060.91	$1,060.85	$1,060.80