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	$11.67	4.209%	$12.1612	$12.16	$12.15	$12.20
Purchase #2	$39.27	11.745%	$43.8823	$43.88	$43.90	$43.90
Purchase #3	$233.70	13.519%	$265.2939	$265.29	$265.30	$265.30
Purchase #4	$192.71	9.763%	$211.5243	$211.52	$211.50	$211.50
Purchase #5	$89.35	5.231%	$94.0239	$94.02	$94.00	$94.00
Purchase #6	$77.53	3.602%	$80.3226	$80.32	$80.30	$80.30
Purchase #7	$229.38	9.113%	$250.2834	$250.28	$250.30	$250.30
7 purchase totals =	$873.61		$957.4916	$957.47	$957.45	$957.50