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	$152.65	8.392%	$165.4604	$165.46	$165.45	$165.50
Purchase #2	$54.63	6.725%	$58.3039	$58.30	$58.30	$58.30
Purchase #3	$230.44	8.110%	$249.1287	$249.13	$249.15	$249.10
Purchase #4	$236.40	12.388%	$265.6852	$265.69	$265.70	$265.70
Purchase #5	$152.81	12.866%	$172.4705	$172.47	$172.45	$172.50
Purchase #6	$81.66	8.766%	$88.8183	$88.82	$88.80	$88.80
Purchase #7	$90.64	10.555%	$100.2071	$100.21	$100.20	$100.20
7 purchase totals =	$999.23		$1,100.0741	$1,100.08	$1,100.05	$1,100.10