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	$35.42	9.269%	$38.7031	$38.70	$38.70	$38.70
Purchase #2	$93.54	7.588%	$100.6378	$100.64	$100.65	$100.60
Purchase #3	$31.77	13.108%	$35.9344	$35.93	$35.95	$35.90
Purchase #4	$37.66	3.603%	$39.0169	$39.02	$39.00	$39.00
Purchase #5	$224.40	11.529%	$250.2711	$250.27	$250.25	$250.30
Purchase #6	$151.28	6.110%	$160.5232	$160.52	$160.50	$160.50
Purchase #7	$174.63	12.297%	$196.1043	$196.10	$196.10	$196.10
7 purchase totals =	$748.70		$821.1908	$821.18	$821.15	$821.10