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	$107.32	11.496%	$119.6575	$119.66	$119.65	$119.70
Purchase #2	$50.92	5.480%	$53.7104	$53.71	$53.70	$53.70
Purchase #3	$190.56	10.417%	$210.4106	$210.41	$210.40	$210.40
Purchase #4	$83.27	11.501%	$92.8469	$92.85	$92.85	$92.80
Purchase #5	$54.52	13.841%	$62.0661	$62.07	$62.05	$62.10
Purchase #6	$29.72	5.754%	$31.4301	$31.43	$31.45	$31.40
Purchase #7	$66.95	3.358%	$69.1982	$69.20	$69.20	$69.20
7 purchase totals =	$583.26		$639.3198	$639.33	$639.30	$639.30