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	$10.85	11.372%	$12.0839	$12.08	$12.10	$12.10
Purchase #2	$245.70	4.299%	$256.2626	$256.26	$256.25	$256.30
Purchase #3	$54.38	10.126%	$59.8865	$59.89	$59.90	$59.90
Purchase #4	$79.89	7.580%	$85.9457	$85.95	$85.95	$85.90
Purchase #5	$87.28	11.702%	$97.4935	$97.49	$97.50	$97.50
Purchase #6	$51.99	13.372%	$58.9421	$58.94	$58.95	$58.90
Purchase #7	$123.38	4.508%	$128.942	$128.94	$128.95	$128.90
7 purchase totals =	$653.47		$699.5563	$699.55	$699.60	$699.50