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	$20.53	8.312%	$22.2365	$22.24	$22.25	$22.20
Purchase #2	$58.51	6.844%	$62.5144	$62.51	$62.50	$62.50
Purchase #3	$90.29	11.701%	$100.8548	$100.85	$100.85	$100.90
Purchase #4	$81.51	9.771%	$89.4743	$89.47	$89.45	$89.50
Purchase #5	$227.95	10.861%	$252.7076	$252.71	$252.70	$252.70
Purchase #6	$221.52	12.689%	$249.6287	$249.63	$249.65	$249.60
Purchase #7	$233.38	4.181%	$243.1376	$243.14	$243.15	$243.10
7 purchase totals =	$933.69		$1,020.5539	$1,020.55	$1,020.55	$1,020.50