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	$74.90	10.584%	$82.8274	$82.83	$82.85	$82.80
Purchase #2	$47.94	7.688%	$51.6256	$51.63	$51.65	$51.60
Purchase #3	$171.76	13.487%	$194.9253	$194.93	$194.95	$194.90
Purchase #4	$239.88	7.710%	$258.3747	$258.37	$258.35	$258.40
Purchase #5	$36.53	9.844%	$40.126	$40.13	$40.15	$40.10
Purchase #6	$6.92	13.388%	$7.8464	$7.85	$7.85	$7.80
Purchase #7	$89.41	4.625%	$93.5452	$93.55	$93.55	$93.50
7 purchase totals =	$667.34		$729.2706	$729.29	$729.35	$729.10