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	$163.66	10.318%	$180.5464	$180.55	$180.55	$180.50
Purchase #2	$107.44	8.305%	$116.3629	$116.36	$116.35	$116.40
Purchase #3	$16.77	12.682%	$18.8968	$18.90	$18.90	$18.90
Purchase #4	$55.33	6.630%	$58.9984	$59.00	$59.00	$59.00
Purchase #5	$74.48	11.860%	$83.3133	$83.31	$83.30	$83.30
Purchase #6	$69.54	11.560%	$77.5788	$77.58	$77.60	$77.60
Purchase #7	$79.81	3.613%	$82.6935	$82.69	$82.70	$82.70
7 purchase totals =	$567.03		$618.3901	$618.39	$618.40	$618.40