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	$29.59	8.453%	$32.0912	$32.09	$32.10	$32.10
Purchase #2	$155.85	9.370%	$170.4531	$170.45	$170.45	$170.50
Purchase #3	$92.43	13.122%	$104.5587	$104.56	$104.55	$104.60
Purchase #4	$42.77	7.380%	$45.9264	$45.93	$45.95	$45.90
Purchase #5	$231.40	5.126%	$243.2616	$243.26	$243.25	$243.30
Purchase #6	$153.98	6.780%	$164.4198	$164.42	$164.40	$164.40
Purchase #7	$104.72	11.652%	$116.922	$116.92	$116.90	$116.90
7 purchase totals =	$810.74		$877.6328	$877.63	$877.60	$877.70