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	$71.37	13.241%	$80.8201	$80.82	$80.80	$80.80
Purchase #2	$87.30	10.834%	$96.7581	$96.76	$96.75	$96.80
Purchase #3	$71.26	10.612%	$78.8221	$78.82	$78.80	$78.80
Purchase #4	$201.55	11.804%	$225.341	$225.34	$225.35	$225.30
Purchase #5	$238.97	8.736%	$259.8464	$259.85	$259.85	$259.80
Purchase #6	$71.62	3.653%	$74.2363	$74.24	$74.25	$74.20
Purchase #7	$217.75	7.356%	$233.7677	$233.77	$233.75	$233.80
7 purchase totals =	$959.82		$1,049.5917	$1,049.60	$1,049.55	$1,049.50