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	$51.88	8.858%	$56.4755	$56.48	$56.50	$56.50
Purchase #2	$15.81	9.231%	$17.2694	$17.27	$17.25	$17.30
Purchase #3	$51.96	7.509%	$55.8617	$55.86	$55.85	$55.90
Purchase #4	$243.32	13.245%	$275.5477	$275.55	$275.55	$275.50
Purchase #5	$220.85	8.453%	$239.5185	$239.52	$239.50	$239.50
Purchase #6	$140.41	10.664%	$155.3833	$155.38	$155.40	$155.40
Purchase #7	$28.88	12.323%	$32.4389	$32.44	$32.45	$32.40
7 purchase totals =	$753.11		$832.4950	$832.50	$832.50	$832.50