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	$96.96	3.531%	$100.3837	$100.38	$100.40	$100.40
Purchase #2	$72.25	11.474%	$80.54	$80.54	$80.55	$80.50
Purchase #3	$96.46	11.780%	$107.823	$107.82	$107.80	$107.80
Purchase #4	$226.59	4.787%	$237.4369	$237.44	$237.45	$237.40
Purchase #5	$126.82	12.372%	$142.5102	$142.51	$142.50	$142.50
Purchase #6	$242.65	6.547%	$258.5363	$258.54	$258.55	$258.50
Purchase #7	$10.50	9.464%	$11.4937	$11.49	$11.50	$11.50
7 purchase totals =	$872.23		$938.7238	$938.72	$938.75	$938.60