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	$50.70	9.507%	$55.52	$55.52	$55.50	$55.50
Purchase #2	$210.64	7.199%	$225.804	$225.80	$225.80	$225.80
Purchase #3	$109.81	13.482%	$124.6146	$124.61	$124.60	$124.60
Purchase #4	$188.26	8.598%	$204.4466	$204.45	$204.45	$204.40
Purchase #5	$142.86	7.200%	$153.1459	$153.15	$153.15	$153.10
Purchase #6	$32.91	13.583%	$37.3802	$37.38	$37.40	$37.40
Purchase #7	$170.95	11.389%	$190.4195	$190.42	$190.40	$190.40
7 purchase totals =	$906.13		$991.3308	$991.33	$991.30	$991.20