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	$165.61	8.439%	$179.5858	$179.59	$179.60	$179.60
Purchase #2	$136.86	6.342%	$145.5397	$145.54	$145.55	$145.50
Purchase #3	$109.39	12.870%	$123.4685	$123.47	$123.45	$123.50
Purchase #4	$8.74	4.685%	$9.1495	$9.15	$9.15	$9.10
Purchase #5	$82.82	9.346%	$90.5604	$90.56	$90.55	$90.60
Purchase #6	$182.74	7.758%	$196.917	$196.92	$196.90	$196.90
Purchase #7	$50.41	3.356%	$52.1018	$52.10	$52.10	$52.10
7 purchase totals =	$736.57		$797.3227	$797.33	$797.30	$797.30