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	$76.75	5.257%	$80.7847	$80.78	$80.80	$80.80
Purchase #2	$126.40	13.252%	$143.1505	$143.15	$143.15	$143.20
Purchase #3	$134.94	6.394%	$143.5681	$143.57	$143.55	$143.60
Purchase #4	$97.46	3.160%	$100.5397	$100.54	$100.55	$100.50
Purchase #5	$130.56	5.874%	$138.2291	$138.23	$138.25	$138.20
Purchase #6	$28.98	3.315%	$29.9407	$29.94	$29.95	$29.90
Purchase #7	$146.79	4.142%	$152.87	$152.87	$152.85	$152.90
7 purchase totals =	$741.88		$789.0828	$789.08	$789.10	$789.10