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	$100.61	6.768%	$107.4193	$107.42	$107.40	$107.40
Purchase #2	$72.88	7.392%	$78.2673	$78.27	$78.25	$78.30
Purchase #3	$153.95	13.353%	$174.5069	$174.51	$174.50	$174.50
Purchase #4	$153.31	8.441%	$166.2509	$166.25	$166.25	$166.30
Purchase #5	$86.96	12.196%	$97.5656	$97.57	$97.55	$97.60
Purchase #6	$63.35	6.479%	$67.4544	$67.45	$67.45	$67.50
Purchase #7	$189.90	7.783%	$204.6799	$204.68	$204.70	$204.70
7 purchase totals =	$820.96		$896.1443	$896.15	$896.10	$896.30