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	$150.45	3.234%	$155.3156	$155.32	$155.30	$155.30
Purchase #2	$137.91	11.269%	$153.4511	$153.45	$153.45	$153.50
Purchase #3	$116.98	10.802%	$129.6162	$129.62	$129.60	$129.60
Purchase #4	$87.97	13.840%	$100.145	$100.15	$100.15	$100.10
Purchase #5	$35.69	11.664%	$39.8529	$39.85	$39.85	$39.90
Purchase #6	$127.92	11.637%	$142.8061	$142.81	$142.80	$142.80
Purchase #7	$148.98	12.228%	$167.1973	$167.20	$167.20	$167.20
7 purchase totals =	$805.90		$888.3842	$888.40	$888.35	$888.40