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	$105.51	12.396%	$118.589	$118.59	$118.60	$118.60
Purchase #2	$142.98	12.834%	$161.3301	$161.33	$161.35	$161.30
Purchase #3	$33.71	7.659%	$36.2918	$36.29	$36.30	$36.30
Purchase #4	$19.56	4.762%	$20.4914	$20.49	$20.50	$20.50
Purchase #5	$16.94	7.616%	$18.2302	$18.23	$18.25	$18.20
Purchase #6	$57.74	12.839%	$65.1532	$65.15	$65.15	$65.20
Purchase #7	$131.39	11.807%	$146.9032	$146.90	$146.90	$146.90
7 purchase totals =	$507.83		$566.9889	$566.98	$567.05	$567.00