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	$72.60	7.213%	$77.8366	$77.84	$77.85	$77.80
Purchase #2	$64.65	8.611%	$70.217	$70.22	$70.20	$70.20
Purchase #3	$47.85	6.459%	$50.9406	$50.94	$50.95	$50.90
Purchase #4	$97.66	11.638%	$109.0257	$109.03	$109.05	$109.00
Purchase #5	$137.87	4.729%	$144.3899	$144.39	$144.40	$144.40
Purchase #6	$233.49	7.204%	$250.3106	$250.31	$250.30	$250.30
Purchase #7	$31.40	13.298%	$35.5756	$35.58	$35.60	$35.60
7 purchase totals =	$685.52		$738.2960	$738.31	$738.35	$738.20