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	$28.69	11.188%	$31.8998	$31.90	$31.90	$31.90
Purchase #2	$206.95	3.704%	$214.6154	$214.62	$214.60	$214.60
Purchase #3	$86.92	4.527%	$90.8549	$90.85	$90.85	$90.90
Purchase #4	$29.63	7.521%	$31.8585	$31.86	$31.85	$31.90
Purchase #5	$74.31	12.778%	$83.8053	$83.81	$83.80	$83.80
Purchase #6	$250.70	4.502%	$261.9865	$261.99	$262.00	$262.00
Purchase #7	$120.47	4.146%	$125.4647	$125.46	$125.45	$125.50
7 purchase totals =	$797.67		$840.4851	$840.49	$840.45	$840.60