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	$36.41	4.334%	$37.988	$37.99	$38.00	$38.00
Purchase #2	$134.54	6.157%	$142.8236	$142.82	$142.80	$142.80
Purchase #3	$196.85	12.315%	$221.0921	$221.09	$221.10	$221.10
Purchase #4	$210.79	6.160%	$223.7747	$223.77	$223.75	$223.80
Purchase #5	$178.78	5.486%	$188.5879	$188.59	$188.60	$188.60
Purchase #6	$9.74	12.127%	$10.9212	$10.92	$10.90	$10.90
Purchase #7	$107.33	7.624%	$115.5128	$115.51	$115.50	$115.50
7 purchase totals =	$874.44		$940.7003	$940.69	$940.65	$940.70