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	$33.91	13.593%	$38.5194	$38.52	$38.50	$38.50
Purchase #2	$93.55	13.109%	$105.8135	$105.81	$105.80	$105.80
Purchase #3	$38.78	9.718%	$42.5486	$42.55	$42.55	$42.50
Purchase #4	$231.88	6.626%	$247.2444	$247.24	$247.25	$247.20
Purchase #5	$233.69	4.268%	$243.6639	$243.66	$243.65	$243.70
Purchase #6	$199.32	12.463%	$224.1613	$224.16	$224.15	$224.20
Purchase #7	$121.82	8.147%	$131.7447	$131.74	$131.75	$131.70
7 purchase totals =	$952.95		$1,033.6958	$1,033.68	$1,033.65	$1,033.60