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	$215.50	8.270%	$233.3219	$233.32	$233.30	$233.30
Purchase #2	$112.97	10.216%	$124.511	$124.51	$124.50	$124.50
Purchase #3	$215.30	5.542%	$227.2319	$227.23	$227.25	$227.20
Purchase #4	$65.69	10.309%	$72.462	$72.46	$72.45	$72.50
Purchase #5	$69.70	5.485%	$73.523	$73.52	$73.50	$73.50
Purchase #6	$140.37	9.435%	$153.6139	$153.61	$153.60	$153.60
Purchase #7	$49.46	7.396%	$53.1181	$53.12	$53.10	$53.10
7 purchase totals =	$868.99		$937.7818	$937.77	$937.70	$937.70