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	$33.71	9.319%	$36.8514	$36.85	$36.85	$36.90
Purchase #2	$187.37	11.751%	$209.3878	$209.39	$209.40	$209.40
Purchase #3	$116.81	10.669%	$129.2725	$129.27	$129.25	$129.30
Purchase #4	$53.44	3.425%	$55.2703	$55.27	$55.25	$55.30
Purchase #5	$95.40	10.732%	$105.6383	$105.64	$105.65	$105.60
Purchase #6	$56.75	13.666%	$64.5055	$64.51	$64.50	$64.50
Purchase #7	$34.52	11.144%	$38.3669	$38.37	$38.35	$38.40
7 purchase totals =	$578.00		$639.2927	$639.30	$639.25	$639.40