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	$146.83	12.772%	$165.5831	$165.58	$165.60	$165.60
Purchase #2	$139.67	9.314%	$152.6789	$152.68	$152.70	$152.70
Purchase #3	$81.89	4.543%	$85.6103	$85.61	$85.60	$85.60
Purchase #4	$243.98	3.385%	$252.2387	$252.24	$252.25	$252.20
Purchase #5	$123.31	3.841%	$128.0463	$128.05	$128.05	$128.00
Purchase #6	$58.28	11.819%	$65.1681	$65.17	$65.15	$65.20
Purchase #7	$159.46	11.769%	$178.2268	$178.23	$178.25	$178.20
7 purchase totals =	$953.42		$1,027.5522	$1,027.56	$1,027.60	$1,027.50