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	$104.57	13.326%	$118.505	$118.51	$118.50	$118.50
Purchase #2	$213.73	5.492%	$225.4681	$225.47	$225.45	$225.50
Purchase #3	$57.45	6.562%	$61.2199	$61.22	$61.20	$61.20
Purchase #4	$115.56	10.257%	$127.413	$127.41	$127.40	$127.40
Purchase #5	$237.47	4.126%	$247.268	$247.27	$247.25	$247.30
Purchase #6	$18.57	6.622%	$19.7997	$19.80	$19.80	$19.80
Purchase #7	$42.64	6.811%	$45.5442	$45.54	$45.55	$45.50
7 purchase totals =	$789.99		$845.2179	$845.22	$845.15	$845.20