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	$80.31	10.406%	$88.6671	$88.67	$88.65	$88.70
Purchase #2	$126.30	9.510%	$138.3111	$138.31	$138.30	$138.30
Purchase #3	$124.74	5.536%	$131.6456	$131.65	$131.65	$131.60
Purchase #4	$117.60	11.643%	$131.2922	$131.29	$131.30	$131.30
Purchase #5	$241.34	5.586%	$254.8213	$254.82	$254.80	$254.80
Purchase #6	$137.28	8.461%	$148.8953	$148.90	$148.90	$148.90
Purchase #7	$182.54	3.694%	$189.283	$189.28	$189.30	$189.30
7 purchase totals =	$1,010.11		$1,082.9156	$1,082.92	$1,082.90	$1,082.90