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	$199.28	13.716%	$226.6132	$226.61	$226.60	$226.60
Purchase #2	$37.67	7.438%	$40.4719	$40.47	$40.45	$40.50
Purchase #3	$87.53	10.640%	$96.8432	$96.84	$96.85	$96.80
Purchase #4	$38.45	8.452%	$41.6998	$41.70	$41.70	$41.70
Purchase #5	$167.34	7.277%	$179.5173	$179.52	$179.50	$179.50
Purchase #6	$41.76	4.166%	$43.4997	$43.50	$43.50	$43.50
Purchase #7	$131.26	11.864%	$146.8327	$146.83	$146.85	$146.80
7 purchase totals =	$703.29		$775.4778	$775.47	$775.45	$775.40