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	$147.74	12.140%	$165.6756	$165.68	$165.70	$165.70
Purchase #2	$143.91	8.699%	$156.4287	$156.43	$156.45	$156.40
Purchase #3	$20.88	3.833%	$21.6803	$21.68	$21.70	$21.70
Purchase #4	$89.35	3.585%	$92.5532	$92.55	$92.55	$92.60
Purchase #5	$53.46	10.427%	$59.0343	$59.03	$59.05	$59.00
Purchase #6	$168.78	6.448%	$179.6629	$179.66	$179.65	$179.70
Purchase #7	$95.64	6.784%	$102.1282	$102.13	$102.15	$102.10
7 purchase totals =	$719.76		$777.1632	$777.16	$777.25	$777.20