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	$98.54	5.103%	$103.5685	$103.57	$103.55	$103.60
Purchase #2	$218.37	11.274%	$242.989	$242.99	$243.00	$243.00
Purchase #3	$108.78	5.638%	$114.913	$114.91	$114.90	$114.90
Purchase #4	$108.69	5.380%	$114.5375	$114.54	$114.55	$114.50
Purchase #5	$123.55	3.259%	$127.5765	$127.58	$127.60	$127.60
Purchase #6	$20.26	4.769%	$21.2262	$21.23	$21.25	$21.20
Purchase #7	$52.81	5.282%	$55.5994	$55.60	$55.60	$55.60
7 purchase totals =	$731.00		$780.4101	$780.42	$780.45	$780.40