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	$95.45	5.329%	$100.5365	$100.54	$100.55	$100.50
Purchase #2	$141.68	4.179%	$147.6008	$147.60	$147.60	$147.60
Purchase #3	$250.75	5.116%	$263.5784	$263.58	$263.60	$263.60
Purchase #4	$193.52	6.389%	$205.884	$205.88	$205.90	$205.90
Purchase #5	$122.98	7.208%	$131.8444	$131.84	$131.85	$131.80
Purchase #6	$212.86	11.823%	$238.0264	$238.03	$238.05	$238.00
Purchase #7	$141.77	3.667%	$146.9687	$146.97	$146.95	$147.00
7 purchase totals =	$1,159.01		$1,234.4392	$1,234.44	$1,234.50	$1,234.40