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	$45.30	4.736%	$47.4454	$47.45	$47.45	$47.40
Purchase #2	$203.29	7.670%	$218.8823	$218.88	$218.90	$218.90
Purchase #3	$85.72	8.321%	$92.8528	$92.85	$92.85	$92.90
Purchase #4	$65.97	3.602%	$68.3462	$68.35	$68.35	$68.30
Purchase #5	$122.76	3.685%	$127.2837	$127.28	$127.30	$127.30
Purchase #6	$151.51	4.630%	$158.5249	$158.52	$158.50	$158.50
Purchase #7	$134.35	13.803%	$152.8943	$152.89	$152.90	$152.90
7 purchase totals =	$808.90		$866.2296	$866.22	$866.25	$866.20