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	$161.52	7.362%	$173.4111	$173.41	$173.40	$173.40
Purchase #2	$61.91	9.573%	$67.8366	$67.84	$67.85	$67.80
Purchase #3	$83.80	6.749%	$89.4557	$89.46	$89.45	$89.50
Purchase #4	$27.96	7.503%	$30.0578	$30.06	$30.05	$30.10
Purchase #5	$68.82	13.732%	$78.2704	$78.27	$78.25	$78.30
Purchase #6	$146.38	13.750%	$166.5073	$166.51	$166.50	$166.50
Purchase #7	$52.37	6.159%	$55.5955	$55.60	$55.60	$55.60
7 purchase totals =	$602.76		$661.1344	$661.15	$661.10	$661.20