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	$198.85	7.823%	$214.406	$214.41	$214.40	$214.40
Purchase #2	$109.85	4.208%	$114.4725	$114.47	$114.45	$114.50
Purchase #3	$224.33	11.722%	$250.626	$250.63	$250.65	$250.60
Purchase #4	$23.74	3.177%	$24.4942	$24.49	$24.50	$24.50
Purchase #5	$99.77	8.392%	$108.1427	$108.14	$108.15	$108.10
Purchase #6	$115.48	6.672%	$123.1848	$123.18	$123.20	$123.20
Purchase #7	$244.77	8.339%	$265.1814	$265.18	$265.20	$265.20
7 purchase totals =	$1,016.79		$1,100.5076	$1,100.50	$1,100.55	$1,100.50