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	$100.76	9.754%	$110.5881	$110.59	$110.60	$110.60
Purchase #2	$59.90	7.710%	$64.5183	$64.52	$64.50	$64.50
Purchase #3	$28.37	10.119%	$31.2408	$31.24	$31.25	$31.20
Purchase #4	$170.79	11.452%	$190.3489	$190.35	$190.35	$190.30
Purchase #5	$97.77	3.834%	$101.5185	$101.52	$101.50	$101.50
Purchase #6	$153.83	12.242%	$172.6619	$172.66	$172.65	$172.70
Purchase #7	$225.91	6.681%	$241.003	$241.00	$241.00	$241.00
7 purchase totals =	$837.33		$911.8795	$911.88	$911.85	$911.80