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	$84.61	6.712%	$90.289	$90.29	$90.30	$90.30
Purchase #2	$163.35	9.862%	$179.4596	$179.46	$179.45	$179.50
Purchase #3	$186.54	5.366%	$196.5497	$196.55	$196.55	$196.50
Purchase #4	$43.28	12.820%	$48.8285	$48.83	$48.85	$48.80
Purchase #5	$158.75	4.471%	$165.8477	$165.85	$165.85	$165.80
Purchase #6	$68.38	13.363%	$77.5176	$77.52	$77.50	$77.50
Purchase #7	$175.31	9.103%	$191.2685	$191.27	$191.25	$191.30
7 purchase totals =	$880.22		$949.7606	$949.77	$949.75	$949.70