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	$100.86	8.797%	$109.7327	$109.73	$109.75	$109.70
Purchase #2	$104.26	12.670%	$117.4697	$117.47	$117.45	$117.50
Purchase #3	$146.56	3.568%	$151.7893	$151.79	$151.80	$151.80
Purchase #4	$82.80	11.671%	$92.4636	$92.46	$92.45	$92.50
Purchase #5	$189.56	5.160%	$199.3413	$199.34	$199.35	$199.30
Purchase #6	$100.51	12.852%	$113.4275	$113.43	$113.45	$113.40
Purchase #7	$74.80	6.128%	$79.3837	$79.38	$79.40	$79.40
7 purchase totals =	$799.35		$863.6078	$863.60	$863.65	$863.60