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	$137.43	12.109%	$154.0714	$154.07	$154.05	$154.10
Purchase #2	$219.38	3.707%	$227.5124	$227.51	$227.50	$227.50
Purchase #3	$33.86	10.359%	$37.3676	$37.37	$37.35	$37.40
Purchase #4	$62.57	8.528%	$67.906	$67.91	$67.90	$67.90
Purchase #5	$150.42	4.554%	$157.2701	$157.27	$157.25	$157.30
Purchase #6	$208.69	4.539%	$218.1624	$218.16	$218.15	$218.20
Purchase #7	$46.72	6.502%	$49.7577	$49.76	$49.75	$49.80
7 purchase totals =	$859.07		$912.0476	$912.05	$911.95	$912.20