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	$49.78	13.831%	$56.6651	$56.67	$56.65	$56.70
Purchase #2	$58.63	6.345%	$62.3501	$62.35	$62.35	$62.40
Purchase #3	$120.34	10.513%	$132.9913	$132.99	$133.00	$133.00
Purchase #4	$53.51	5.415%	$56.4076	$56.41	$56.40	$56.40
Purchase #5	$59.45	5.817%	$62.9082	$62.91	$62.90	$62.90
Purchase #6	$92.71	6.192%	$98.4506	$98.45	$98.45	$98.50
Purchase #7	$179.28	9.791%	$196.8333	$196.83	$196.85	$196.80
7 purchase totals =	$613.70		$666.6062	$666.61	$666.60	$666.70