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	$52.88	6.843%	$56.4986	$56.50	$56.50	$56.50
Purchase #2	$210.32	11.699%	$234.9253	$234.93	$234.95	$234.90
Purchase #3	$214.29	13.411%	$243.0284	$243.03	$243.05	$243.00
Purchase #4	$42.27	8.579%	$45.8963	$45.90	$45.90	$45.90
Purchase #5	$63.85	10.856%	$70.7816	$70.78	$70.80	$70.80
Purchase #6	$114.91	3.866%	$119.3524	$119.35	$119.35	$119.40
Purchase #7	$73.73	5.497%	$77.7829	$77.78	$77.80	$77.80
7 purchase totals =	$772.25		$848.2655	$848.27	$848.35	$848.30