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	$174.76	9.750%	$191.7991	$191.80	$191.80	$191.80
Purchase #2	$189.35	5.451%	$199.6715	$199.67	$199.65	$199.70
Purchase #3	$131.99	10.123%	$145.3513	$145.35	$145.35	$145.40
Purchase #4	$46.45	8.801%	$50.5381	$50.54	$50.55	$50.50
Purchase #5	$86.90	4.450%	$90.7671	$90.77	$90.75	$90.80
Purchase #6	$126.73	10.484%	$140.0164	$140.02	$140.00	$140.00
Purchase #7	$187.37	6.274%	$199.1256	$199.13	$199.15	$199.10
7 purchase totals =	$943.55		$1,017.2691	$1,017.28	$1,017.25	$1,017.30