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	$132.90	8.271%	$143.8922	$143.89	$143.90	$143.90
Purchase #2	$87.68	10.772%	$97.1249	$97.12	$97.10	$97.10
Purchase #3	$173.39	10.641%	$191.8404	$191.84	$191.85	$191.80
Purchase #4	$89.94	6.340%	$95.6422	$95.64	$95.65	$95.60
Purchase #5	$134.25	3.631%	$139.1246	$139.12	$139.10	$139.10
Purchase #6	$96.50	13.129%	$109.1695	$109.17	$109.15	$109.20
Purchase #7	$84.59	13.793%	$96.2575	$96.26	$96.25	$96.30
7 purchase totals =	$799.25		$873.0513	$873.04	$873.00	$873.00