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	$170.41	6.193%	$180.9635	$180.96	$180.95	$181.00
Purchase #2	$81.72	4.597%	$85.4767	$85.48	$85.50	$85.50
Purchase #3	$190.59	8.345%	$206.4947	$206.49	$206.50	$206.50
Purchase #4	$18.93	4.108%	$19.7076	$19.71	$19.70	$19.70
Purchase #5	$36.57	6.383%	$38.9043	$38.90	$38.90	$38.90
Purchase #6	$139.59	13.237%	$158.0675	$158.07	$158.05	$158.10
Purchase #7	$136.92	10.401%	$151.161	$151.16	$151.15	$151.20
7 purchase totals =	$774.73		$840.7753	$840.77	$840.75	$840.90