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	$66.27	7.626%	$71.3238	$71.32	$71.30	$71.30
Purchase #2	$36.45	5.432%	$38.43	$38.43	$38.45	$38.40
Purchase #3	$139.61	6.775%	$149.0686	$149.07	$149.05	$149.10
Purchase #4	$13.79	3.231%	$14.2356	$14.24	$14.25	$14.20
Purchase #5	$173.51	10.573%	$191.8552	$191.86	$191.85	$191.90
Purchase #6	$59.47	3.605%	$61.6139	$61.61	$61.60	$61.60
Purchase #7	$149.78	8.582%	$162.6341	$162.63	$162.65	$162.60
7 purchase totals =	$638.88		$689.1612	$689.16	$689.15	$689.10