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	$96.65	11.107%	$107.3849	$107.38	$107.40	$107.40
Purchase #2	$83.34	7.753%	$89.8014	$89.80	$89.80	$89.80
Purchase #3	$68.81	6.652%	$73.3872	$73.39	$73.40	$73.40
Purchase #4	$50.66	4.687%	$53.0344	$53.03	$53.05	$53.00
Purchase #5	$19.96	3.765%	$20.7115	$20.71	$20.70	$20.70
Purchase #6	$190.86	10.662%	$211.2095	$211.21	$211.20	$211.20
Purchase #7	$92.99	13.248%	$105.3093	$105.31	$105.30	$105.30
7 purchase totals =	$603.27		$660.8382	$660.83	$660.85	$660.80