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	$179.88	10.477%	$198.726	$198.73	$198.75	$198.70
Purchase #2	$90.63	7.668%	$97.5795	$97.58	$97.60	$97.60
Purchase #3	$170.39	11.745%	$190.4023	$190.40	$190.40	$190.40
Purchase #4	$226.51	7.642%	$243.8199	$243.82	$243.80	$243.80
Purchase #5	$40.94	10.212%	$45.1208	$45.12	$45.10	$45.10
Purchase #6	$150.94	13.168%	$170.8158	$170.82	$170.80	$170.80
Purchase #7	$239.64	13.471%	$271.9219	$271.92	$271.90	$271.90
7 purchase totals =	$1,098.93		$1,218.3862	$1,218.39	$1,218.35	$1,218.30