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	$163.88	5.165%	$172.3444	$172.34	$172.35	$172.30
Purchase #2	$39.31	8.163%	$42.5189	$42.52	$42.50	$42.50
Purchase #3	$33.43	13.475%	$37.9347	$37.93	$37.95	$37.90
Purchase #4	$179.40	7.402%	$192.6792	$192.68	$192.70	$192.70
Purchase #5	$129.66	12.181%	$145.4539	$145.45	$145.45	$145.50
Purchase #6	$15.89	5.732%	$16.8008	$16.80	$16.80	$16.80
Purchase #7	$66.27	8.523%	$71.9182	$71.92	$71.90	$71.90
7 purchase totals =	$627.84		$679.6501	$679.64	$679.65	$679.60