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	$81.28	9.826%	$89.2666	$89.27	$89.25	$89.30
Purchase #2	$228.49	13.243%	$258.7489	$258.75	$258.75	$258.70
Purchase #3	$33.47	3.755%	$34.7268	$34.73	$34.75	$34.70
Purchase #4	$223.34	13.530%	$253.5579	$253.56	$253.55	$253.60
Purchase #5	$129.28	13.597%	$146.8582	$146.86	$146.85	$146.90
Purchase #6	$160.35	8.614%	$174.1625	$174.16	$174.15	$174.20
Purchase #7	$52.90	12.313%	$59.4136	$59.41	$59.40	$59.40
7 purchase totals =	$909.11		$1,016.7345	$1,016.74	$1,016.70	$1,016.80