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	$9.86	8.436%	$10.6918	$10.69	$10.70	$10.70
Purchase #2	$244.32	3.738%	$253.4527	$253.45	$253.45	$253.50
Purchase #3	$40.86	13.845%	$46.5171	$46.52	$46.50	$46.50
Purchase #4	$6.70	6.373%	$7.127	$7.13	$7.15	$7.10
Purchase #5	$230.65	9.789%	$253.2283	$253.23	$253.25	$253.20
Purchase #6	$95.54	4.187%	$99.5403	$99.54	$99.55	$99.50
Purchase #7	$182.73	9.829%	$200.6905	$200.69	$200.70	$200.70
7 purchase totals =	$810.66		$871.2477	$871.25	$871.30	$871.20