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	$233.41	10.172%	$257.1525	$257.15	$257.15	$257.20
Purchase #2	$88.79	5.411%	$93.5944	$93.59	$93.60	$93.60
Purchase #3	$249.36	13.711%	$283.5497	$283.55	$283.55	$283.50
Purchase #4	$167.44	4.304%	$174.6466	$174.65	$174.65	$174.60
Purchase #5	$51.50	11.202%	$57.269	$57.27	$57.25	$57.30
Purchase #6	$92.50	13.452%	$104.9431	$104.94	$104.95	$104.90
Purchase #7	$99.93	11.390%	$111.312	$111.31	$111.30	$111.30
7 purchase totals =	$982.93		$1,082.4673	$1,082.46	$1,082.45	$1,082.40