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	$172.53	4.617%	$180.4957	$180.50	$180.50	$180.50
Purchase #2	$177.73	8.830%	$193.4236	$193.42	$193.40	$193.40
Purchase #3	$7.52	3.751%	$7.8021	$7.80	$7.80	$7.80
Purchase #4	$117.95	8.195%	$127.616	$127.62	$127.60	$127.60
Purchase #5	$38.33	7.107%	$41.0541	$41.05	$41.05	$41.10
Purchase #6	$57.60	3.734%	$59.7508	$59.75	$59.75	$59.80
Purchase #7	$217.49	7.271%	$233.3037	$233.30	$233.30	$233.30
7 purchase totals =	$789.15		$843.4460	$843.44	$843.40	$843.50