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	$61.86	7.371%	$66.4197	$66.42	$66.40	$66.40
Purchase #2	$125.91	13.192%	$142.52	$142.52	$142.50	$142.50
Purchase #3	$93.34	4.294%	$97.348	$97.35	$97.35	$97.30
Purchase #4	$89.28	6.128%	$94.7511	$94.75	$94.75	$94.80
Purchase #5	$55.80	11.488%	$62.2103	$62.21	$62.20	$62.20
Purchase #6	$205.27	11.287%	$228.4388	$228.44	$228.45	$228.40
Purchase #7	$103.59	7.263%	$111.1137	$111.11	$111.10	$111.10
7 purchase totals =	$735.05		$802.8016	$802.80	$802.75	$802.70