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	$58.51	13.476%	$66.3948	$66.39	$66.40	$66.40
Purchase #2	$238.83	11.615%	$266.5701	$266.57	$266.55	$266.60
Purchase #3	$190.51	10.696%	$210.8869	$210.89	$210.90	$210.90
Purchase #4	$123.85	13.783%	$140.9202	$140.92	$140.90	$140.90
Purchase #5	$152.25	10.277%	$167.8967	$167.90	$167.90	$167.90
Purchase #6	$200.75	7.106%	$215.0153	$215.02	$215.00	$215.00
Purchase #7	$146.44	13.218%	$165.7964	$165.80	$165.80	$165.80
7 purchase totals =	$1,111.14		$1,233.4804	$1,233.49	$1,233.45	$1,233.50