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	$118.61	7.164%	$127.1072	$127.11	$127.10	$127.10
Purchase #2	$29.38	12.704%	$33.1124	$33.11	$33.10	$33.10
Purchase #3	$119.81	3.735%	$124.2849	$124.28	$124.30	$124.30
Purchase #4	$135.76	6.712%	$144.8722	$144.87	$144.85	$144.90
Purchase #5	$129.94	11.224%	$144.5245	$144.52	$144.50	$144.50
Purchase #6	$50.77	6.856%	$54.2508	$54.25	$54.25	$54.30
Purchase #7	$15.90	8.316%	$17.2222	$17.22	$17.20	$17.20
7 purchase totals =	$600.17		$645.3742	$645.36	$645.30	$645.40