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	$170.70	5.190%	$179.5593	$179.56	$179.55	$179.60
Purchase #2	$225.94	10.341%	$249.3045	$249.30	$249.30	$249.30
Purchase #3	$10.37	3.199%	$10.7017	$10.70	$10.70	$10.70
Purchase #4	$66.61	9.174%	$72.7208	$72.72	$72.70	$72.70
Purchase #5	$80.92	4.441%	$84.5137	$84.51	$84.50	$84.50
Purchase #6	$112.84	13.300%	$127.8477	$127.85	$127.85	$127.80
Purchase #7	$170.54	6.452%	$181.5432	$181.54	$181.55	$181.50
7 purchase totals =	$837.92		$906.1909	$906.18	$906.15	$906.10