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	$90.84	9.662%	$99.617	$99.62	$99.60	$99.60
Purchase #2	$75.49	4.630%	$78.9852	$78.99	$79.00	$79.00
Purchase #3	$164.45	11.513%	$183.3831	$183.38	$183.40	$183.40
Purchase #4	$69.69	12.323%	$78.2779	$78.28	$78.30	$78.30
Purchase #5	$48.36	11.547%	$53.9441	$53.94	$53.95	$53.90
Purchase #6	$92.25	9.585%	$101.0922	$101.09	$101.10	$101.10
Purchase #7	$100.86	9.651%	$110.594	$110.59	$110.60	$110.60
7 purchase totals =	$641.94		$705.8935	$705.89	$705.95	$705.90