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	$89.28	11.429%	$99.4838	$99.48	$99.50	$99.50
Purchase #2	$107.32	12.696%	$120.9453	$120.95	$120.95	$120.90
Purchase #3	$152.49	10.306%	$168.2056	$168.21	$168.20	$168.20
Purchase #4	$116.62	13.799%	$132.7124	$132.71	$132.70	$132.70
Purchase #5	$59.50	11.209%	$66.1694	$66.17	$66.15	$66.20
Purchase #6	$238.52	12.739%	$268.9051	$268.91	$268.90	$268.90
Purchase #7	$38.33	6.201%	$40.7068	$40.71	$40.70	$40.70
7 purchase totals =	$802.06		$897.1284	$897.14	$897.10	$897.10