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	$9.71	4.360%	$10.1334	$10.13	$10.15	$10.10
Purchase #2	$241.87	3.183%	$249.5687	$249.57	$249.55	$249.60
Purchase #3	$168.60	12.848%	$190.2617	$190.26	$190.25	$190.30
Purchase #4	$120.60	4.759%	$126.3394	$126.34	$126.35	$126.30
Purchase #5	$65.54	10.638%	$72.5121	$72.51	$72.50	$72.50
Purchase #6	$148.33	7.483%	$159.4295	$159.43	$159.45	$159.40
Purchase #7	$62.88	12.281%	$70.6023	$70.60	$70.60	$70.60
7 purchase totals =	$817.53		$878.8471	$878.84	$878.85	$878.80