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	$102.90	13.567%	$116.8604	$116.86	$116.85	$116.90
Purchase #2	$247.44	13.671%	$281.2675	$281.27	$281.25	$281.30
Purchase #3	$105.41	11.677%	$117.7187	$117.72	$117.70	$117.70
Purchase #4	$80.72	6.346%	$85.8425	$85.84	$85.85	$85.80
Purchase #5	$60.62	10.116%	$66.7523	$66.75	$66.75	$66.80
Purchase #6	$94.73	5.363%	$99.8104	$99.81	$99.80	$99.80
Purchase #7	$190.82	5.181%	$200.7064	$200.71	$200.70	$200.70
7 purchase totals =	$882.64		$968.9582	$968.96	$968.90	$969.00