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	$13.66	12.722%	$15.3978	$15.40	$15.40	$15.40
Purchase #2	$127.27	12.588%	$143.2907	$143.29	$143.30	$143.30
Purchase #3	$154.53	3.301%	$159.631	$159.63	$159.65	$159.60
Purchase #4	$172.27	13.695%	$195.8624	$195.86	$195.85	$195.90
Purchase #5	$27.92	6.332%	$29.6879	$29.69	$29.70	$29.70
Purchase #6	$52.89	13.274%	$59.9106	$59.91	$59.90	$59.90
Purchase #7	$101.48	8.175%	$109.776	$109.78	$109.80	$109.80
7 purchase totals =	$650.02		$713.5564	$713.56	$713.60	$713.60