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	$70.39	5.672%	$74.3825	$74.38	$74.40	$74.40
Purchase #2	$45.57	13.511%	$51.727	$51.73	$51.75	$51.70
Purchase #3	$56.42	5.861%	$59.7268	$59.73	$59.75	$59.70
Purchase #4	$212.55	3.393%	$219.7618	$219.76	$219.75	$219.80
Purchase #5	$163.50	13.616%	$185.7622	$185.76	$185.75	$185.80
Purchase #6	$207.59	8.619%	$225.4822	$225.48	$225.50	$225.50
Purchase #7	$38.69	4.418%	$40.3993	$40.40	$40.40	$40.40
7 purchase totals =	$794.71		$857.2418	$857.24	$857.30	$857.30