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	$123.62	4.179%	$128.7861	$128.79	$128.80	$128.80
Purchase #2	$144.37	10.568%	$159.627	$159.63	$159.65	$159.60
Purchase #3	$9.55	9.761%	$10.4822	$10.48	$10.50	$10.50
Purchase #4	$100.39	8.860%	$109.2846	$109.28	$109.30	$109.30
Purchase #5	$43.55	3.830%	$45.218	$45.22	$45.20	$45.20
Purchase #6	$89.28	3.109%	$92.0557	$92.06	$92.05	$92.10
Purchase #7	$19.74	11.551%	$22.0202	$22.02	$22.00	$22.00
7 purchase totals =	$530.50		$567.4738	$567.48	$567.50	$567.50