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	$222.62	12.799%	$251.1131	$251.11	$251.10	$251.10
Purchase #2	$124.41	13.540%	$141.2551	$141.26	$141.25	$141.30
Purchase #3	$128.28	10.267%	$141.4505	$141.45	$141.45	$141.50
Purchase #4	$9.54	10.435%	$10.5355	$10.54	$10.55	$10.50
Purchase #5	$84.49	5.595%	$89.2172	$89.22	$89.20	$89.20
Purchase #6	$193.51	3.135%	$199.5765	$199.58	$199.60	$199.60
Purchase #7	$136.60	5.836%	$144.572	$144.57	$144.55	$144.60
7 purchase totals =	$899.45		$977.7199	$977.73	$977.70	$977.80