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	$241.52	13.519%	$274.1711	$274.17	$274.15	$274.20
Purchase #2	$242.34	4.509%	$253.2671	$253.27	$253.25	$253.30
Purchase #3	$80.91	11.872%	$90.5156	$90.52	$90.50	$90.50
Purchase #4	$203.31	13.315%	$230.3807	$230.38	$230.40	$230.40
Purchase #5	$50.82	13.624%	$57.7437	$57.74	$57.75	$57.70
Purchase #6	$27.55	8.830%	$29.9827	$29.98	$30.00	$30.00
Purchase #7	$159.38	13.813%	$181.3952	$181.40	$181.40	$181.40
7 purchase totals =	$1,005.83		$1,117.4561	$1,117.46	$1,117.45	$1,117.50