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	$178.92	5.200%	$188.2238	$188.22	$188.20	$188.20
Purchase #2	$133.50	7.349%	$143.3109	$143.31	$143.30	$143.30
Purchase #3	$10.32	11.562%	$11.5132	$11.51	$11.50	$11.50
Purchase #4	$71.83	10.627%	$79.4634	$79.46	$79.45	$79.50
Purchase #5	$104.67	6.313%	$111.2778	$111.28	$111.30	$111.30
Purchase #6	$195.54	4.515%	$204.3686	$204.37	$204.35	$204.40
Purchase #7	$69.86	13.530%	$79.3121	$79.31	$79.30	$79.30
7 purchase totals =	$764.64		$817.4698	$817.46	$817.40	$817.50