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	$19.62	7.726%	$21.1358	$21.14	$21.15	$21.10
Purchase #2	$34.28	11.392%	$38.1852	$38.19	$38.20	$38.20
Purchase #3	$59.33	6.784%	$63.3549	$63.35	$63.35	$63.40
Purchase #4	$128.25	10.145%	$141.261	$141.26	$141.25	$141.30
Purchase #5	$136.94	4.690%	$143.3625	$143.36	$143.35	$143.40
Purchase #6	$44.30	4.751%	$46.4047	$46.40	$46.40	$46.40
Purchase #7	$83.47	7.218%	$89.4949	$89.49	$89.50	$89.50
7 purchase totals =	$506.19		$543.1990	$543.19	$543.20	$543.30