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	$244.40	5.847%	$258.6901	$258.69	$258.70	$258.70
Purchase #2	$35.29	10.252%	$38.9079	$38.91	$38.90	$38.90
Purchase #3	$9.89	9.711%	$10.8504	$10.85	$10.85	$10.90
Purchase #4	$20.46	7.376%	$21.9691	$21.97	$21.95	$22.00
Purchase #5	$134.31	3.704%	$139.2848	$139.28	$139.30	$139.30
Purchase #6	$134.32	10.230%	$148.0609	$148.06	$148.05	$148.10
Purchase #7	$150.90	3.655%	$156.4154	$156.42	$156.40	$156.40
7 purchase totals =	$729.57		$774.1786	$774.18	$774.15	$774.30