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	$57.93	4.190%	$60.3573	$60.36	$60.35	$60.40
Purchase #2	$235.84	11.313%	$262.5206	$262.52	$262.50	$262.50
Purchase #3	$107.80	3.295%	$111.352	$111.35	$111.35	$111.40
Purchase #4	$66.25	11.413%	$73.8111	$73.81	$73.80	$73.80
Purchase #5	$223.92	11.611%	$249.9194	$249.92	$249.90	$249.90
Purchase #6	$120.75	11.661%	$134.8307	$134.83	$134.85	$134.80
Purchase #7	$86.54	3.369%	$89.4555	$89.46	$89.45	$89.50
7 purchase totals =	$899.03		$982.2466	$982.25	$982.20	$982.30