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	$238.38	13.638%	$270.8903	$270.89	$270.90	$270.90
Purchase #2	$199.67	4.546%	$208.747	$208.75	$208.75	$208.70
Purchase #3	$62.80	3.411%	$64.9421	$64.94	$64.95	$64.90
Purchase #4	$48.28	9.539%	$52.8854	$52.89	$52.90	$52.90
Purchase #5	$145.84	5.707%	$154.1631	$154.16	$154.15	$154.20
Purchase #6	$157.38	10.363%	$173.6893	$173.69	$173.70	$173.70
Purchase #7	$72.31	11.455%	$80.5931	$80.59	$80.60	$80.60
7 purchase totals =	$924.66		$1,005.9103	$1,005.91	$1,005.95	$1,005.90