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	$184.60	8.811%	$200.8651	$200.87	$200.85	$200.90
Purchase #2	$72.88	10.141%	$80.2708	$80.27	$80.25	$80.30
Purchase #3	$22.60	12.594%	$25.4462	$25.45	$25.45	$25.40
Purchase #4	$94.94	9.716%	$104.1644	$104.16	$104.15	$104.20
Purchase #5	$30.31	13.269%	$34.3318	$34.33	$34.35	$34.30
Purchase #6	$39.55	9.372%	$43.2566	$43.26	$43.25	$43.30
Purchase #7	$101.98	10.206%	$112.3881	$112.39	$112.40	$112.40
7 purchase totals =	$546.86		$600.7230	$600.73	$600.70	$600.80