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	$37.65	7.607%	$40.514	$40.51	$40.50	$40.50
Purchase #2	$228.99	5.517%	$241.6234	$241.62	$241.60	$241.60
Purchase #3	$72.73	6.335%	$77.3374	$77.34	$77.35	$77.30
Purchase #4	$223.95	8.657%	$243.3374	$243.34	$243.35	$243.30
Purchase #5	$124.99	5.474%	$131.832	$131.83	$131.85	$131.80
Purchase #6	$34.47	8.764%	$37.491	$37.49	$37.50	$37.50
Purchase #7	$86.54	4.288%	$90.2508	$90.25	$90.25	$90.30
7 purchase totals =	$809.32		$862.3860	$862.38	$862.40	$862.30