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	$34.68	12.229%	$38.921	$38.92	$38.90	$38.90
Purchase #2	$123.55	13.172%	$139.824	$139.82	$139.80	$139.80
Purchase #3	$144.76	12.353%	$162.6422	$162.64	$162.65	$162.60
Purchase #4	$145.31	10.858%	$161.0878	$161.09	$161.10	$161.10
Purchase #5	$148.32	9.627%	$162.5988	$162.60	$162.60	$162.60
Purchase #6	$203.79	13.657%	$231.6216	$231.62	$231.60	$231.60
Purchase #7	$146.92	8.865%	$159.9445	$159.94	$159.95	$159.90
7 purchase totals =	$947.33		$1,056.6399	$1,056.63	$1,056.60	$1,056.50