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	$164.66	4.675%	$172.3579	$172.36	$172.35	$172.40
Purchase #2	$250.38	5.492%	$264.1309	$264.13	$264.15	$264.10
Purchase #3	$118.29	4.264%	$123.3339	$123.33	$123.35	$123.30
Purchase #4	$42.53	7.641%	$45.7797	$45.78	$45.80	$45.80
Purchase #5	$22.54	12.251%	$25.3014	$25.30	$25.30	$25.30
Purchase #6	$228.62	12.457%	$257.0992	$257.10	$257.10	$257.10
Purchase #7	$72.69	13.630%	$82.5976	$82.60	$82.60	$82.60
7 purchase totals =	$899.71		$970.6006	$970.60	$970.65	$970.60