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	$60.28	13.675%	$68.5233	$68.52	$68.50	$68.50
Purchase #2	$63.92	6.405%	$68.0141	$68.01	$68.00	$68.00
Purchase #3	$160.60	4.230%	$167.3934	$167.39	$167.40	$167.40
Purchase #4	$42.25	6.769%	$45.1099	$45.11	$45.10	$45.10
Purchase #5	$72.75	13.114%	$82.2904	$82.29	$82.30	$82.30
Purchase #6	$207.94	11.208%	$231.2459	$231.25	$231.25	$231.20
Purchase #7	$41.25	3.526%	$42.7045	$42.70	$42.70	$42.70
7 purchase totals =	$648.99		$705.2815	$705.27	$705.25	$705.20