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	$183.27	12.138%	$205.5153	$205.52	$205.50	$205.50
Purchase #2	$233.69	6.179%	$248.1297	$248.13	$248.15	$248.10
Purchase #3	$118.86	6.723%	$126.851	$126.85	$126.85	$126.90
Purchase #4	$79.37	13.592%	$90.158	$90.16	$90.15	$90.20
Purchase #5	$195.53	8.501%	$212.152	$212.15	$212.15	$212.20
Purchase #6	$81.71	8.294%	$88.487	$88.49	$88.50	$88.50
Purchase #7	$204.34	11.860%	$228.5747	$228.57	$228.55	$228.60
7 purchase totals =	$1,096.77		$1,199.8677	$1,199.87	$1,199.85	$1,200.00