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	$33.96	9.565%	$37.2083	$37.21	$37.20	$37.20
Purchase #2	$127.35	13.365%	$144.3703	$144.37	$144.35	$144.40
Purchase #3	$167.52	13.627%	$190.348	$190.35	$190.35	$190.30
Purchase #4	$91.46	3.743%	$94.8833	$94.88	$94.90	$94.90
Purchase #5	$91.51	13.856%	$104.1896	$104.19	$104.20	$104.20
Purchase #6	$10.27	5.661%	$10.8514	$10.85	$10.85	$10.90
Purchase #7	$154.58	4.724%	$161.8824	$161.88	$161.90	$161.90
7 purchase totals =	$676.65		$743.7333	$743.73	$743.75	$743.80