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	$210.73	9.575%	$230.9074	$230.91	$230.90	$230.90
Purchase #2	$66.57	3.713%	$69.0417	$69.04	$69.05	$69.00
Purchase #3	$40.46	4.607%	$42.324	$42.32	$42.30	$42.30
Purchase #4	$136.38	6.305%	$144.9788	$144.98	$145.00	$145.00
Purchase #5	$169.84	6.122%	$180.2376	$180.24	$180.25	$180.20
Purchase #6	$107.72	3.582%	$111.5785	$111.58	$111.60	$111.60
Purchase #7	$90.53	9.407%	$99.0462	$99.05	$99.05	$99.00
7 purchase totals =	$822.23		$878.1142	$878.12	$878.15	$878.00