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	$56.91	3.412%	$58.8518	$58.85	$58.85	$58.90
Purchase #2	$200.56	13.339%	$227.3127	$227.31	$227.30	$227.30
Purchase #3	$103.89	8.293%	$112.5056	$112.51	$112.50	$112.50
Purchase #4	$71.42	9.536%	$78.2306	$78.23	$78.25	$78.20
Purchase #5	$56.57	5.222%	$59.5241	$59.52	$59.50	$59.50
Purchase #6	$181.35	10.323%	$200.0708	$200.07	$200.05	$200.10
Purchase #7	$101.68	8.649%	$110.4743	$110.47	$110.45	$110.50
7 purchase totals =	$772.38		$846.9699	$846.96	$846.90	$847.00