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	$9.55	6.441%	$10.1651	$10.17	$10.15	$10.20
Purchase #2	$92.64	12.179%	$103.9226	$103.92	$103.90	$103.90
Purchase #3	$99.94	11.352%	$111.2852	$111.29	$111.30	$111.30
Purchase #4	$70.77	10.242%	$78.0183	$78.02	$78.00	$78.00
Purchase #5	$104.96	12.447%	$118.0244	$118.02	$118.00	$118.00
Purchase #6	$71.68	4.806%	$75.1249	$75.12	$75.10	$75.10
Purchase #7	$128.54	12.771%	$144.9558	$144.96	$144.95	$145.00
7 purchase totals =	$578.08		$641.4963	$641.50	$641.40	$641.50