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	$37.31	6.667%	$39.7975	$39.80	$39.80	$39.80
Purchase #2	$222.93	3.680%	$231.1338	$231.13	$231.15	$231.10
Purchase #3	$67.46	4.455%	$70.4653	$70.47	$70.45	$70.50
Purchase #4	$96.64	8.746%	$105.0921	$105.09	$105.10	$105.10
Purchase #5	$138.46	9.712%	$151.9072	$151.91	$151.90	$151.90
Purchase #6	$244.81	13.720%	$278.3979	$278.40	$278.40	$278.40
Purchase #7	$80.61	5.561%	$85.0927	$85.09	$85.10	$85.10
7 purchase totals =	$888.22		$961.8865	$961.89	$961.90	$961.90