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	$192.46	11.837%	$215.2415	$215.24	$215.25	$215.20
Purchase #2	$156.59	10.773%	$173.4594	$173.46	$173.45	$173.50
Purchase #3	$59.79	3.426%	$61.8384	$61.84	$61.85	$61.80
Purchase #4	$126.90	11.351%	$141.3044	$141.30	$141.30	$141.30
Purchase #5	$15.34	10.159%	$16.8984	$16.90	$16.90	$16.90
Purchase #6	$59.28	9.713%	$65.0379	$65.04	$65.05	$65.00
Purchase #7	$102.28	6.568%	$108.9978	$109.00	$109.00	$109.00
7 purchase totals =	$712.64		$782.7778	$782.78	$782.80	$782.70