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	$165.80	11.675%	$185.1572	$185.16	$185.15	$185.20
Purchase #2	$172.91	9.244%	$188.8938	$188.89	$188.90	$188.90
Purchase #3	$97.57	12.381%	$109.6501	$109.65	$109.65	$109.70
Purchase #4	$83.52	7.778%	$90.0162	$90.02	$90.00	$90.00
Purchase #5	$30.31	12.749%	$34.1742	$34.17	$34.15	$34.20
Purchase #6	$152.42	11.752%	$170.3324	$170.33	$170.35	$170.30
Purchase #7	$22.67	3.238%	$23.4041	$23.40	$23.40	$23.40
7 purchase totals =	$725.20		$801.6280	$801.62	$801.60	$801.70