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	$155.85	6.250%	$165.5906	$165.59	$165.60	$165.60
Purchase #2	$34.51	12.667%	$38.8814	$38.88	$38.90	$38.90
Purchase #3	$148.73	6.859%	$158.9314	$158.93	$158.95	$158.90
Purchase #4	$138.72	5.747%	$146.6922	$146.69	$146.70	$146.70
Purchase #5	$91.36	10.487%	$100.9409	$100.94	$100.95	$100.90
Purchase #6	$20.41	7.705%	$21.9826	$21.98	$22.00	$22.00
Purchase #7	$200.77	13.615%	$228.1048	$228.10	$228.10	$228.10
7 purchase totals =	$790.35		$861.1239	$861.11	$861.20	$861.10