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	$250.69	13.638%	$284.8791	$284.88	$284.90	$284.90
Purchase #2	$114.48	11.586%	$127.7437	$127.74	$127.75	$127.70
Purchase #3	$132.48	12.790%	$149.4242	$149.42	$149.40	$149.40
Purchase #4	$152.31	3.287%	$157.3164	$157.32	$157.30	$157.30
Purchase #5	$99.97	5.275%	$105.2434	$105.24	$105.25	$105.20
Purchase #6	$37.69	10.102%	$41.4974	$41.50	$41.50	$41.50
Purchase #7	$167.91	11.291%	$186.8687	$186.87	$186.85	$186.90
7 purchase totals =	$955.53		$1,052.9729	$1,052.97	$1,052.95	$1,052.90