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	$134.67	10.280%	$148.5141	$148.51	$148.50	$148.50
Purchase #2	$33.78	13.559%	$38.3602	$38.36	$38.35	$38.40
Purchase #3	$57.96	8.234%	$62.7324	$62.73	$62.75	$62.70
Purchase #4	$55.97	6.171%	$59.4239	$59.42	$59.40	$59.40
Purchase #5	$94.45	6.639%	$100.7205	$100.72	$100.70	$100.70
Purchase #6	$250.29	6.517%	$266.6014	$266.60	$266.60	$266.60
Purchase #7	$158.55	10.773%	$175.6306	$175.63	$175.65	$175.60
7 purchase totals =	$785.67		$851.9831	$851.97	$851.95	$851.90