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	$72.46	8.225%	$78.4198	$78.42	$78.40	$78.40
Purchase #2	$75.38	3.435%	$77.9693	$77.97	$77.95	$78.00
Purchase #3	$214.37	12.396%	$240.9433	$240.94	$240.95	$240.90
Purchase #4	$217.81	12.611%	$245.278	$245.28	$245.30	$245.30
Purchase #5	$139.82	10.161%	$154.0271	$154.03	$154.05	$154.00
Purchase #6	$17.91	11.439%	$19.9587	$19.96	$19.95	$20.00
Purchase #7	$233.77	12.766%	$263.6131	$263.61	$263.60	$263.60
7 purchase totals =	$971.52		$1,080.2093	$1,080.21	$1,080.20	$1,080.20