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	$17.34	6.838%	$18.5257	$18.53	$18.55	$18.50
Purchase #2	$92.69	3.449%	$95.8869	$95.89	$95.90	$95.90
Purchase #3	$16.65	5.645%	$17.5899	$17.59	$17.60	$17.60
Purchase #4	$228.54	4.363%	$238.5112	$238.51	$238.50	$238.50
Purchase #5	$36.42	13.404%	$41.3017	$41.30	$41.30	$41.30
Purchase #6	$132.49	13.501%	$150.3775	$150.38	$150.40	$150.40
Purchase #7	$177.93	7.624%	$191.4954	$191.50	$191.50	$191.50
7 purchase totals =	$702.06		$753.6883	$753.70	$753.75	$753.70