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	$94.45	6.665%	$100.7451	$100.75	$100.75	$100.70
Purchase #2	$159.30	11.517%	$177.6466	$177.65	$177.65	$177.60
Purchase #3	$171.25	4.734%	$179.357	$179.36	$179.35	$179.40
Purchase #4	$58.53	10.492%	$64.671	$64.67	$64.65	$64.70
Purchase #5	$144.45	13.699%	$164.2382	$164.24	$164.25	$164.20
Purchase #6	$86.71	3.176%	$89.4639	$89.46	$89.45	$89.50
Purchase #7	$128.54	9.829%	$141.1742	$141.17	$141.15	$141.20
7 purchase totals =	$843.23		$917.2960	$917.30	$917.25	$917.30