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	$18.47	10.150%	$20.3447	$20.34	$20.35	$20.30
Purchase #2	$107.48	4.770%	$112.6068	$112.61	$112.60	$112.60
Purchase #3	$103.89	5.130%	$109.2196	$109.22	$109.20	$109.20
Purchase #4	$123.46	6.494%	$131.4775	$131.48	$131.50	$131.50
Purchase #5	$205.90	13.209%	$233.0973	$233.10	$233.10	$233.10
Purchase #6	$212.64	10.784%	$235.5711	$235.57	$235.55	$235.60
Purchase #7	$107.98	13.700%	$122.7733	$122.77	$122.75	$122.80
7 purchase totals =	$879.82		$965.0903	$965.09	$965.05	$965.10