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	$17.30	13.114%	$19.5687	$19.57	$19.55	$19.60
Purchase #2	$151.38	13.651%	$172.0449	$172.04	$172.05	$172.00
Purchase #3	$84.71	8.788%	$92.1543	$92.15	$92.15	$92.20
Purchase #4	$121.59	4.743%	$127.357	$127.36	$127.35	$127.40
Purchase #5	$89.66	6.831%	$95.7847	$95.78	$95.80	$95.80
Purchase #6	$92.42	12.300%	$103.7877	$103.79	$103.80	$103.80
Purchase #7	$55.71	11.692%	$62.2236	$62.22	$62.20	$62.20
7 purchase totals =	$612.77		$672.9209	$672.91	$672.90	$673.00