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	$57.44	3.768%	$59.6043	$59.60	$59.60	$59.60
Purchase #2	$215.74	11.589%	$240.7421	$240.74	$240.75	$240.70
Purchase #3	$123.87	13.334%	$140.3868	$140.39	$140.40	$140.40
Purchase #4	$135.45	12.422%	$152.2756	$152.28	$152.30	$152.30
Purchase #5	$127.89	3.405%	$132.2447	$132.24	$132.25	$132.20
Purchase #6	$154.68	11.656%	$172.7095	$172.71	$172.70	$172.70
Purchase #7	$17.81	13.230%	$20.1663	$20.17	$20.15	$20.20
7 purchase totals =	$832.88		$918.1293	$918.13	$918.15	$918.10