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	$18.94	9.662%	$20.77	$20.77	$20.75	$20.80
Purchase #2	$32.83	3.451%	$33.963	$33.96	$33.95	$34.00
Purchase #3	$94.71	5.265%	$99.6965	$99.70	$99.70	$99.70
Purchase #4	$83.71	7.149%	$89.6944	$89.69	$89.70	$89.70
Purchase #5	$51.91	10.776%	$57.5038	$57.50	$57.50	$57.50
Purchase #6	$48.61	10.448%	$53.6888	$53.69	$53.70	$53.70
Purchase #7	$90.49	6.202%	$96.1022	$96.10	$96.10	$96.10
7 purchase totals =	$421.20		$451.4187	$451.41	$451.40	$451.50