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	$92.45	8.297%	$100.1206	$100.12	$100.10	$100.10
Purchase #2	$132.89	9.470%	$145.4747	$145.47	$145.45	$145.50
Purchase #3	$185.34	5.213%	$195.0018	$195.00	$195.00	$195.00
Purchase #4	$104.60	8.521%	$113.513	$113.51	$113.50	$113.50
Purchase #5	$118.39	4.440%	$123.6465	$123.65	$123.65	$123.60
Purchase #6	$102.77	5.623%	$108.5488	$108.55	$108.55	$108.50
Purchase #7	$248.34	8.792%	$270.1741	$270.17	$270.15	$270.20
7 purchase totals =	$984.78		$1,056.4795	$1,056.47	$1,056.40	$1,056.40