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	$149.50	11.132%	$166.1423	$166.14	$166.15	$166.10
Purchase #2	$104.66	9.865%	$114.9847	$114.98	$115.00	$115.00
Purchase #3	$29.50	13.256%	$33.4105	$33.41	$33.40	$33.40
Purchase #4	$114.47	11.451%	$127.578	$127.58	$127.60	$127.60
Purchase #5	$93.39	12.332%	$104.9069	$104.91	$104.90	$104.90
Purchase #6	$79.87	12.503%	$89.8561	$89.86	$89.85	$89.90
Purchase #7	$13.39	6.729%	$14.291	$14.29	$14.30	$14.30
7 purchase totals =	$584.78		$651.1695	$651.17	$651.20	$651.20