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	$231.74	7.413%	$248.9189	$248.92	$248.90	$248.90
Purchase #2	$160.48	11.726%	$179.2979	$179.30	$179.30	$179.30
Purchase #3	$63.93	6.584%	$68.1392	$68.14	$68.15	$68.10
Purchase #4	$56.55	5.854%	$59.8604	$59.86	$59.85	$59.90
Purchase #5	$190.84	11.500%	$212.7866	$212.79	$212.80	$212.80
Purchase #6	$102.77	8.187%	$111.1838	$111.18	$111.20	$111.20
Purchase #7	$92.81	11.397%	$103.3876	$103.39	$103.40	$103.40
7 purchase totals =	$899.12		$983.5744	$983.58	$983.60	$983.60