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	$103.93	6.213%	$110.3872	$110.39	$110.40	$110.40
Purchase #2	$46.92	13.745%	$53.3692	$53.37	$53.35	$53.40
Purchase #3	$63.45	11.185%	$70.5469	$70.55	$70.55	$70.50
Purchase #4	$217.67	11.591%	$242.9001	$242.90	$242.90	$242.90
Purchase #5	$221.84	3.454%	$229.5024	$229.50	$229.50	$229.50
Purchase #6	$100.94	10.526%	$111.5649	$111.56	$111.55	$111.60
Purchase #7	$66.25	5.685%	$70.0163	$70.02	$70.00	$70.00
7 purchase totals =	$821.00		$888.2870	$888.29	$888.25	$888.30