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	$209.80	9.302%	$229.3156	$229.32	$229.30	$229.30
Purchase #2	$191.39	4.176%	$199.3824	$199.38	$199.40	$199.40
Purchase #3	$188.49	10.339%	$207.978	$207.98	$208.00	$208.00
Purchase #4	$39.55	12.564%	$44.5191	$44.52	$44.50	$44.50
Purchase #5	$103.78	7.294%	$111.3497	$111.35	$111.35	$111.30
Purchase #6	$56.51	3.493%	$58.4839	$58.48	$58.50	$58.50
Purchase #7	$49.27	11.444%	$54.9085	$54.91	$54.90	$54.90
7 purchase totals =	$838.79		$905.9372	$905.94	$905.95	$905.90