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	$249.98	10.189%	$275.4505	$275.45	$275.45	$275.50
Purchase #2	$57.90	10.599%	$64.0368	$64.04	$64.05	$64.00
Purchase #3	$157.58	8.702%	$171.2926	$171.29	$171.30	$171.30
Purchase #4	$174.25	9.244%	$190.3577	$190.36	$190.35	$190.40
Purchase #5	$37.36	9.268%	$40.8225	$40.82	$40.80	$40.80
Purchase #6	$24.80	11.570%	$27.6694	$27.67	$27.65	$27.70
Purchase #7	$112.62	13.353%	$127.6581	$127.66	$127.65	$127.70
7 purchase totals =	$814.49		$897.2876	$897.29	$897.25	$897.40