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	$160.40	13.288%	$181.714	$181.71	$181.70	$181.70
Purchase #2	$239.52	7.264%	$256.9187	$256.92	$256.90	$256.90
Purchase #3	$214.35	5.142%	$225.3719	$225.37	$225.35	$225.40
Purchase #4	$171.34	10.688%	$189.6528	$189.65	$189.65	$189.70
Purchase #5	$190.89	11.200%	$212.2697	$212.27	$212.25	$212.30
Purchase #6	$112.90	13.846%	$128.5321	$128.53	$128.55	$128.50
Purchase #7	$141.47	3.610%	$146.5771	$146.58	$146.60	$146.60
7 purchase totals =	$1,230.87		$1,341.0363	$1,341.03	$1,341.00	$1,341.10