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	$151.67	10.224%	$167.1767	$167.18	$167.20	$167.20
Purchase #2	$55.80	12.692%	$62.8821	$62.88	$62.90	$62.90
Purchase #3	$140.50	5.722%	$148.5394	$148.54	$148.55	$148.50
Purchase #4	$125.52	4.222%	$130.8195	$130.82	$130.80	$130.80
Purchase #5	$173.57	5.501%	$183.1181	$183.12	$183.10	$183.10
Purchase #6	$106.40	5.741%	$112.5084	$112.51	$112.50	$112.50
Purchase #7	$52.79	4.106%	$54.9576	$54.96	$54.95	$55.00
7 purchase totals =	$806.25		$860.0018	$860.01	$860.00	$860.00