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	$228.39	11.751%	$255.2281	$255.23	$255.25	$255.20
Purchase #2	$74.92	11.874%	$83.816	$83.82	$83.80	$83.80
Purchase #3	$189.29	8.241%	$204.8894	$204.89	$204.90	$204.90
Purchase #4	$127.37	3.770%	$132.1718	$132.17	$132.15	$132.20
Purchase #5	$124.77	4.680%	$130.6092	$130.61	$130.60	$130.60
Purchase #6	$79.79	9.668%	$87.5041	$87.50	$87.50	$87.50
Purchase #7	$39.64	10.782%	$43.914	$43.91	$43.90	$43.90
7 purchase totals =	$864.17		$938.1326	$938.13	$938.10	$938.10