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	$206.95	5.588%	$218.5144	$218.51	$218.50	$218.50
Purchase #2	$138.56	8.315%	$150.0813	$150.08	$150.10	$150.10
Purchase #3	$173.42	3.443%	$179.3909	$179.39	$179.40	$179.40
Purchase #4	$123.26	5.835%	$130.4522	$130.45	$130.45	$130.50
Purchase #5	$112.32	13.731%	$127.7427	$127.74	$127.75	$127.70
Purchase #6	$35.71	3.140%	$36.8313	$36.83	$36.85	$36.80
Purchase #7	$14.26	6.834%	$15.2345	$15.23	$15.25	$15.20
7 purchase totals =	$804.48		$858.2473	$858.23	$858.30	$858.20