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	$174.67	8.732%	$189.9222	$189.92	$189.90	$189.90
Purchase #2	$94.94	11.294%	$105.6625	$105.66	$105.65	$105.70
Purchase #3	$184.58	9.677%	$202.4418	$202.44	$202.45	$202.40
Purchase #4	$121.91	4.584%	$127.4984	$127.50	$127.50	$127.50
Purchase #5	$168.70	7.346%	$181.0927	$181.09	$181.10	$181.10
Purchase #6	$80.72	12.155%	$90.5315	$90.53	$90.55	$90.50
Purchase #7	$75.95	4.688%	$79.5105	$79.51	$79.50	$79.50
7 purchase totals =	$901.47		$976.6596	$976.65	$976.65	$976.60