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	$10.68	11.505%	$11.9087	$11.91	$11.90	$11.90
Purchase #2	$24.39	13.243%	$27.62	$27.62	$27.60	$27.60
Purchase #3	$136.40	11.791%	$152.4829	$152.48	$152.50	$152.50
Purchase #4	$51.85	13.157%	$58.6719	$58.67	$58.65	$58.70
Purchase #5	$130.78	11.206%	$145.4352	$145.44	$145.45	$145.40
Purchase #6	$15.43	5.274%	$16.2438	$16.24	$16.25	$16.20
Purchase #7	$38.82	4.385%	$40.5223	$40.52	$40.50	$40.50
7 purchase totals =	$408.35		$452.8848	$452.88	$452.85	$452.80