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	$61.69	6.336%	$65.5987	$65.60	$65.60	$65.60
Purchase #2	$143.79	3.338%	$148.5897	$148.59	$148.60	$148.60
Purchase #3	$210.51	5.135%	$221.3197	$221.32	$221.30	$221.30
Purchase #4	$39.68	7.246%	$42.5552	$42.56	$42.55	$42.60
Purchase #5	$32.47	7.110%	$34.7786	$34.78	$34.80	$34.80
Purchase #6	$203.77	4.835%	$213.6223	$213.62	$213.60	$213.60
Purchase #7	$128.41	10.796%	$142.2731	$142.27	$142.25	$142.30
7 purchase totals =	$820.32		$868.7373	$868.74	$868.70	$868.80