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	$89.66	11.332%	$99.8203	$99.82	$99.80	$99.80
Purchase #2	$161.38	11.112%	$179.3125	$179.31	$179.30	$179.30
Purchase #3	$178.94	3.726%	$185.6073	$185.61	$185.60	$185.60
Purchase #4	$60.49	4.551%	$63.2429	$63.24	$63.25	$63.20
Purchase #5	$70.41	3.862%	$73.1292	$73.13	$73.15	$73.10
Purchase #6	$138.60	5.587%	$146.3436	$146.34	$146.35	$146.30
Purchase #7	$237.37	5.794%	$251.1232	$251.12	$251.10	$251.10
7 purchase totals =	$936.85		$998.5790	$998.57	$998.55	$998.40