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	$83.61	7.838%	$90.1634	$90.16	$90.15	$90.20
Purchase #2	$24.82	5.109%	$26.0881	$26.09	$26.10	$26.10
Purchase #3	$11.59	7.435%	$12.4517	$12.45	$12.45	$12.50
Purchase #4	$56.32	11.784%	$62.9567	$62.96	$62.95	$63.00
Purchase #5	$42.36	13.377%	$48.0265	$48.03	$48.05	$48.00
Purchase #6	$111.67	11.412%	$124.4138	$124.41	$124.40	$124.40
Purchase #7	$162.33	7.366%	$174.2872	$174.29	$174.30	$174.30
7 purchase totals =	$492.70		$538.3874	$538.39	$538.40	$538.50