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	$242.72	9.756%	$266.3998	$266.40	$266.40	$266.40
Purchase #2	$17.46	10.626%	$19.3153	$19.32	$19.30	$19.30
Purchase #3	$229.52	12.756%	$258.7976	$258.80	$258.80	$258.80
Purchase #4	$66.89	5.499%	$70.5683	$70.57	$70.55	$70.60
Purchase #5	$206.47	13.194%	$233.7117	$233.71	$233.70	$233.70
Purchase #6	$200.66	13.740%	$228.2307	$228.23	$228.25	$228.20
Purchase #7	$219.74	6.428%	$233.8649	$233.86	$233.85	$233.90
7 purchase totals =	$1,183.46		$1,310.8883	$1,310.89	$1,310.85	$1,310.90