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	$54.54	12.517%	$61.3668	$61.37	$61.35	$61.40
Purchase #2	$178.80	10.504%	$197.5812	$197.58	$197.60	$197.60
Purchase #3	$18.68	11.606%	$20.848	$20.85	$20.85	$20.80
Purchase #4	$27.54	6.482%	$29.3251	$29.33	$29.35	$29.30
Purchase #5	$74.52	5.222%	$78.4114	$78.41	$78.40	$78.40
Purchase #6	$61.54	10.734%	$68.1457	$68.15	$68.15	$68.10
Purchase #7	$92.29	7.402%	$99.1213	$99.12	$99.10	$99.10
7 purchase totals =	$507.91		$554.7995	$554.81	$554.80	$554.70