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	$78.76	6.133%	$83.5904	$83.59	$83.60	$83.60
Purchase #2	$22.72	7.365%	$24.3933	$24.39	$24.40	$24.40
Purchase #3	$100.82	10.143%	$111.0462	$111.05	$111.05	$111.00
Purchase #4	$204.28	13.166%	$231.1755	$231.18	$231.20	$231.20
Purchase #5	$239.41	4.520%	$250.2313	$250.23	$250.25	$250.20
Purchase #6	$150.81	10.236%	$166.2469	$166.25	$166.25	$166.20
Purchase #7	$68.56	9.146%	$74.8305	$74.83	$74.85	$74.80
7 purchase totals =	$865.36		$941.5141	$941.52	$941.60	$941.40