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	$32.77	6.279%	$34.8276	$34.83	$34.85	$34.80
Purchase #2	$67.27	10.188%	$74.1235	$74.12	$74.10	$74.10
Purchase #3	$80.64	11.479%	$89.8967	$89.90	$89.90	$89.90
Purchase #4	$176.29	5.477%	$185.9454	$185.95	$185.95	$185.90
Purchase #5	$74.47	13.797%	$84.7446	$84.74	$84.75	$84.70
Purchase #6	$75.38	13.366%	$85.4553	$85.46	$85.45	$85.50
Purchase #7	$183.64	3.558%	$190.1739	$190.17	$190.15	$190.20
7 purchase totals =	$690.46		$745.1670	$745.17	$745.15	$745.10