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	$64.41	12.368%	$72.3762	$72.38	$72.40	$72.40
Purchase #2	$76.44	5.332%	$80.5158	$80.52	$80.50	$80.50
Purchase #3	$92.29	12.282%	$103.6251	$103.63	$103.65	$103.60
Purchase #4	$28.52	3.841%	$29.6155	$29.62	$29.60	$29.60
Purchase #5	$231.83	10.658%	$256.5384	$256.54	$256.55	$256.50
Purchase #6	$190.32	12.145%	$213.4344	$213.43	$213.45	$213.40
Purchase #7	$222.81	6.426%	$237.1278	$237.13	$237.15	$237.10
7 purchase totals =	$906.62		$993.2332	$993.25	$993.30	$993.10