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	$13.83	13.854%	$15.746	$15.75	$15.75	$15.70
Purchase #2	$166.51	7.239%	$178.5637	$178.56	$178.55	$178.60
Purchase #3	$37.89	4.293%	$39.5166	$39.52	$39.50	$39.50
Purchase #4	$193.69	10.839%	$214.6841	$214.68	$214.70	$214.70
Purchase #5	$177.66	12.314%	$199.5371	$199.54	$199.55	$199.50
Purchase #6	$157.48	5.388%	$165.965	$165.97	$165.95	$166.00
Purchase #7	$177.49	6.206%	$188.505	$188.51	$188.50	$188.50
7 purchase totals =	$924.55		$1,002.5175	$1,002.53	$1,002.50	$1,002.50