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	$228.87	6.647%	$244.083	$244.08	$244.10	$244.10
Purchase #2	$174.71	4.557%	$182.6715	$182.67	$182.65	$182.70
Purchase #3	$29.96	10.572%	$33.1274	$33.13	$33.15	$33.10
Purchase #4	$143.46	5.623%	$151.5268	$151.53	$151.55	$151.50
Purchase #5	$60.40	9.527%	$66.1543	$66.15	$66.15	$66.20
Purchase #6	$105.32	6.859%	$112.5439	$112.54	$112.55	$112.50
Purchase #7	$46.58	5.800%	$49.2816	$49.28	$49.30	$49.30
7 purchase totals =	$789.30		$839.3885	$839.38	$839.45	$839.40