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	$87.98	12.740%	$99.1887	$99.19	$99.20	$99.20
Purchase #2	$111.79	8.137%	$120.8864	$120.89	$120.90	$120.90
Purchase #3	$172.26	13.168%	$194.9432	$194.94	$194.95	$194.90
Purchase #4	$9.41	5.402%	$9.9183	$9.92	$9.90	$9.90
Purchase #5	$204.28	6.841%	$218.2548	$218.25	$218.25	$218.30
Purchase #6	$197.56	8.719%	$214.7853	$214.79	$214.80	$214.80
Purchase #7	$104.54	6.695%	$111.539	$111.54	$111.55	$111.50
7 purchase totals =	$887.82		$969.5157	$969.52	$969.55	$969.50