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	$111.51	9.750%	$122.3822	$122.38	$122.40	$122.40
Purchase #2	$149.64	4.403%	$156.2286	$156.23	$156.25	$156.20
Purchase #3	$42.53	7.646%	$45.7818	$45.78	$45.80	$45.80
Purchase #4	$121.68	4.628%	$127.3114	$127.31	$127.30	$127.30
Purchase #5	$89.90	10.711%	$99.5292	$99.53	$99.55	$99.50
Purchase #6	$161.68	5.721%	$170.9297	$170.93	$170.95	$170.90
Purchase #7	$113.68	8.565%	$123.4167	$123.42	$123.40	$123.40
7 purchase totals =	$790.62		$845.5796	$845.58	$845.65	$845.50