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	$36.95	12.295%	$41.493	$41.49	$41.50	$41.50
Purchase #2	$126.83	8.616%	$137.7577	$137.76	$137.75	$137.80
Purchase #3	$85.25	4.756%	$89.3045	$89.30	$89.30	$89.30
Purchase #4	$24.36	10.190%	$26.8423	$26.84	$26.85	$26.80
Purchase #5	$84.42	8.378%	$91.4927	$91.49	$91.50	$91.50
Purchase #6	$50.31	8.482%	$54.5773	$54.58	$54.60	$54.60
Purchase #7	$118.93	8.400%	$128.9201	$128.92	$128.90	$128.90
7 purchase totals =	$527.05		$570.3876	$570.38	$570.40	$570.40