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	$199.34	5.548%	$210.3994	$210.40	$210.40	$210.40
Purchase #2	$61.36	11.422%	$68.3685	$68.37	$68.35	$68.40
Purchase #3	$35.43	13.656%	$40.2683	$40.27	$40.25	$40.30
Purchase #4	$38.66	12.512%	$43.4971	$43.50	$43.50	$43.50
Purchase #5	$41.72	9.395%	$45.6396	$45.64	$45.65	$45.60
Purchase #6	$112.74	12.799%	$127.1696	$127.17	$127.15	$127.20
Purchase #7	$76.95	3.490%	$79.6356	$79.64	$79.65	$79.60
7 purchase totals =	$566.20		$614.9781	$614.99	$614.95	$615.00