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	$37.46	12.843%	$42.271	$42.27	$42.25	$42.30
Purchase #2	$118.98	7.511%	$127.9166	$127.92	$127.90	$127.90
Purchase #3	$68.83	8.116%	$74.4162	$74.42	$74.40	$74.40
Purchase #4	$86.25	7.621%	$92.8231	$92.82	$92.80	$92.80
Purchase #5	$7.91	7.825%	$8.529	$8.53	$8.55	$8.50
Purchase #6	$48.80	10.490%	$53.9191	$53.92	$53.90	$53.90
Purchase #7	$126.81	8.670%	$137.8044	$137.80	$137.80	$137.80
7 purchase totals =	$495.04		$537.6794	$537.68	$537.60	$537.60