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	$190.94	6.624%	$203.5879	$203.59	$203.60	$203.60
Purchase #2	$98.91	5.109%	$103.9633	$103.96	$103.95	$104.00
Purchase #3	$39.56	6.599%	$42.1706	$42.17	$42.15	$42.20
Purchase #4	$169.69	7.560%	$182.5186	$182.52	$182.50	$182.50
Purchase #5	$110.41	5.153%	$116.0994	$116.10	$116.10	$116.10
Purchase #6	$173.62	13.262%	$196.6455	$196.65	$196.65	$196.60
Purchase #7	$109.34	12.436%	$122.9375	$122.94	$122.95	$122.90
7 purchase totals =	$892.47		$967.9228	$967.93	$967.90	$967.90