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	$207.46	7.176%	$222.3473	$222.35	$222.35	$222.30
Purchase #2	$128.44	12.329%	$144.2754	$144.28	$144.30	$144.30
Purchase #3	$95.42	10.506%	$105.4448	$105.44	$105.45	$105.40
Purchase #4	$13.42	8.162%	$14.5153	$14.52	$14.50	$14.50
Purchase #5	$49.31	12.493%	$55.4703	$55.47	$55.45	$55.50
Purchase #6	$89.76	12.844%	$101.2888	$101.29	$101.30	$101.30
Purchase #7	$6.40	9.642%	$7.0171	$7.02	$7.00	$7.00
7 purchase totals =	$590.21		$650.3590	$650.37	$650.35	$650.30