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	$61.61	5.377%	$64.9228	$64.92	$64.90	$64.90
Purchase #2	$93.88	9.249%	$102.563	$102.56	$102.55	$102.60
Purchase #3	$18.43	12.687%	$20.7682	$20.77	$20.75	$20.80
Purchase #4	$34.94	12.505%	$39.3092	$39.31	$39.30	$39.30
Purchase #5	$74.38	12.223%	$83.4715	$83.47	$83.45	$83.50
Purchase #6	$163.81	4.440%	$171.0832	$171.08	$171.10	$171.10
Purchase #7	$126.67	10.800%	$140.3504	$140.35	$140.35	$140.40
7 purchase totals =	$573.72		$622.4683	$622.46	$622.40	$622.60