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	$168.77	13.475%	$191.5118	$191.51	$191.50	$191.50
Purchase #2	$206.63	8.798%	$224.8093	$224.81	$224.80	$224.80
Purchase #3	$127.38	8.768%	$138.5487	$138.55	$138.55	$138.50
Purchase #4	$25.62	9.718%	$28.1098	$28.11	$28.10	$28.10
Purchase #5	$127.44	3.532%	$131.9412	$131.94	$131.95	$131.90
Purchase #6	$73.35	11.150%	$81.5285	$81.53	$81.55	$81.50
Purchase #7	$155.89	10.871%	$172.8368	$172.84	$172.85	$172.80
7 purchase totals =	$885.08		$969.2861	$969.29	$969.30	$969.10