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	$142.73	4.728%	$149.4783	$149.48	$149.50	$149.50
Purchase #2	$92.46	7.703%	$99.5822	$99.58	$99.60	$99.60
Purchase #3	$111.88	10.413%	$123.5301	$123.53	$123.55	$123.50
Purchase #4	$170.55	11.466%	$190.1053	$190.11	$190.10	$190.10
Purchase #5	$24.59	7.212%	$26.3634	$26.36	$26.35	$26.40
Purchase #6	$168.45	6.381%	$179.1988	$179.20	$179.20	$179.20
Purchase #7	$94.54	5.699%	$99.9278	$99.93	$99.95	$99.90
7 purchase totals =	$805.20		$868.1859	$868.19	$868.25	$868.20