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	$12.35	12.181%	$13.8544	$13.85	$13.85	$13.90
Purchase #2	$60.99	7.282%	$65.4313	$65.43	$65.45	$65.40
Purchase #3	$222.72	12.417%	$250.3751	$250.38	$250.40	$250.40
Purchase #4	$42.54	4.336%	$44.3845	$44.38	$44.40	$44.40
Purchase #5	$51.97	13.219%	$58.8399	$58.84	$58.85	$58.80
Purchase #6	$57.88	13.200%	$65.5202	$65.52	$65.50	$65.50
Purchase #7	$29.98	6.307%	$31.8708	$31.87	$31.85	$31.90
7 purchase totals =	$478.43		$530.2762	$530.27	$530.30	$530.30