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	$47.70	5.223%	$50.1914	$50.19	$50.20	$50.20
Purchase #2	$184.55	8.192%	$199.6683	$199.67	$199.65	$199.70
Purchase #3	$135.49	12.620%	$152.5888	$152.59	$152.60	$152.60
Purchase #4	$123.90	9.161%	$135.2505	$135.25	$135.25	$135.30
Purchase #5	$128.46	3.150%	$132.5065	$132.51	$132.50	$132.50
Purchase #6	$50.51	3.687%	$52.3723	$52.37	$52.35	$52.40
Purchase #7	$105.58	5.723%	$111.6223	$111.62	$111.60	$111.60
7 purchase totals =	$776.19		$834.2001	$834.20	$834.15	$834.30