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	$151.83	13.402%	$172.1783	$172.18	$172.20	$172.20
Purchase #2	$121.88	9.408%	$133.3465	$133.35	$133.35	$133.30
Purchase #3	$218.56	7.469%	$234.8842	$234.88	$234.90	$234.90
Purchase #4	$112.91	13.304%	$127.9315	$127.93	$127.95	$127.90
Purchase #5	$31.65	8.430%	$34.3181	$34.32	$34.30	$34.30
Purchase #6	$88.38	8.189%	$95.6174	$95.62	$95.60	$95.60
Purchase #7	$11.43	9.778%	$12.5476	$12.55	$12.55	$12.50
7 purchase totals =	$736.64		$810.8236	$810.83	$810.85	$810.70