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	$237.66	13.857%	$270.5925	$270.59	$270.60	$270.60
Purchase #2	$44.32	9.180%	$48.3886	$48.39	$48.40	$48.40
Purchase #3	$148.67	12.475%	$167.2166	$167.22	$167.20	$167.20
Purchase #4	$208.41	7.594%	$224.2367	$224.24	$224.25	$224.20
Purchase #5	$97.47	3.108%	$100.4994	$100.50	$100.50	$100.50
Purchase #6	$145.47	5.139%	$152.9457	$152.95	$152.95	$152.90
Purchase #7	$145.46	7.415%	$156.2459	$156.25	$156.25	$156.20
7 purchase totals =	$1,027.46		$1,120.1254	$1,120.14	$1,120.15	$1,120.00