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	$33.43	10.813%	$37.0448	$37.04	$37.05	$37.00
Purchase #2	$29.51	5.465%	$31.1227	$31.12	$31.10	$31.10
Purchase #3	$90.99	5.510%	$96.0035	$96.00	$96.00	$96.00
Purchase #4	$123.72	12.209%	$138.825	$138.83	$138.85	$138.80
Purchase #5	$82.83	4.568%	$86.6137	$86.61	$86.60	$86.60
Purchase #6	$68.54	10.217%	$75.5427	$75.54	$75.55	$75.50
Purchase #7	$71.60	9.325%	$78.2767	$78.28	$78.30	$78.30
7 purchase totals =	$500.62		$543.4291	$543.42	$543.45	$543.30