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	$78.82	6.423%	$83.8826	$83.88	$83.90	$83.90
Purchase #2	$122.97	9.613%	$134.7911	$134.79	$134.80	$134.80
Purchase #3	$135.54	8.103%	$146.5228	$146.52	$146.50	$146.50
Purchase #4	$82.69	13.864%	$94.1541	$94.15	$94.15	$94.20
Purchase #5	$165.78	11.784%	$185.3155	$185.32	$185.30	$185.30
Purchase #6	$192.43	3.613%	$199.3825	$199.38	$199.40	$199.40
Purchase #7	$238.25	7.601%	$256.3594	$256.36	$256.35	$256.40
7 purchase totals =	$1,016.48		$1,100.4080	$1,100.40	$1,100.40	$1,100.50