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	$49.49	6.559%	$52.736	$52.74	$52.75	$52.70
Purchase #2	$101.69	10.579%	$112.4478	$112.45	$112.45	$112.40
Purchase #3	$66.92	5.654%	$70.7037	$70.70	$70.70	$70.70
Purchase #4	$141.51	7.718%	$152.4317	$152.43	$152.45	$152.40
Purchase #5	$57.69	12.345%	$64.8118	$64.81	$64.80	$64.80
Purchase #6	$62.72	4.353%	$65.4502	$65.45	$65.45	$65.50
Purchase #7	$35.99	11.510%	$40.1324	$40.13	$40.15	$40.10
7 purchase totals =	$516.01		$558.7136	$558.71	$558.75	$558.60