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	$246.64	5.665%	$260.6122	$260.61	$260.60	$260.60
Purchase #2	$158.59	7.409%	$170.3399	$170.34	$170.35	$170.30
Purchase #3	$86.74	3.509%	$89.7837	$89.78	$89.80	$89.80
Purchase #4	$81.86	10.163%	$90.1794	$90.18	$90.20	$90.20
Purchase #5	$183.33	7.230%	$196.5848	$196.58	$196.60	$196.60
Purchase #6	$165.61	4.231%	$172.617	$172.62	$172.60	$172.60
Purchase #7	$239.81	5.777%	$253.6638	$253.66	$253.65	$253.70
7 purchase totals =	$1,162.58		$1,233.7808	$1,233.77	$1,233.80	$1,233.80