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	$20.76	8.359%	$22.4953	$22.50	$22.50	$22.50
Purchase #2	$242.87	13.171%	$274.8584	$274.86	$274.85	$274.90
Purchase #3	$112.83	12.812%	$127.2858	$127.29	$127.30	$127.30
Purchase #4	$76.75	10.489%	$84.8003	$84.80	$84.80	$84.80
Purchase #5	$133.54	5.649%	$141.0837	$141.08	$141.10	$141.10
Purchase #6	$124.94	11.766%	$139.6404	$139.64	$139.65	$139.60
Purchase #7	$43.53	4.776%	$45.609	$45.61	$45.60	$45.60
7 purchase totals =	$755.22		$835.7729	$835.78	$835.80	$835.80