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	$99.35	4.582%	$103.9022	$103.90	$103.90	$103.90
Purchase #2	$113.98	11.594%	$127.1948	$127.19	$127.20	$127.20
Purchase #3	$51.49	11.443%	$57.382	$57.38	$57.40	$57.40
Purchase #4	$190.58	10.495%	$210.5814	$210.58	$210.60	$210.60
Purchase #5	$172.40	6.811%	$184.1422	$184.14	$184.15	$184.10
Purchase #6	$221.53	8.710%	$240.8253	$240.83	$240.85	$240.80
Purchase #7	$26.43	5.802%	$27.9635	$27.96	$27.95	$28.00
7 purchase totals =	$875.76		$951.9914	$951.98	$952.05	$952.00