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	$65.60	6.762%	$70.0359	$70.04	$70.05	$70.00
Purchase #2	$239.27	11.507%	$266.8028	$266.80	$266.80	$266.80
Purchase #3	$112.41	13.115%	$127.1526	$127.15	$127.15	$127.20
Purchase #4	$205.88	11.182%	$228.9015	$228.90	$228.90	$228.90
Purchase #5	$124.59	3.111%	$128.466	$128.47	$128.45	$128.50
Purchase #6	$210.82	9.640%	$231.143	$231.14	$231.15	$231.10
Purchase #7	$103.72	13.445%	$117.6652	$117.67	$117.65	$117.70
7 purchase totals =	$1,062.29		$1,170.1670	$1,170.17	$1,170.15	$1,170.20