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	$91.44	8.573%	$99.2792	$99.28	$99.30	$99.30
Purchase #2	$43.85	13.758%	$49.8829	$49.88	$49.90	$49.90
Purchase #3	$15.79	10.531%	$17.4528	$17.45	$17.45	$17.50
Purchase #4	$157.88	7.592%	$169.8662	$169.87	$169.85	$169.90
Purchase #5	$68.56	4.194%	$71.4354	$71.44	$71.45	$71.40
Purchase #6	$165.32	3.768%	$171.5493	$171.55	$171.55	$171.50
Purchase #7	$133.39	12.756%	$150.4052	$150.41	$150.40	$150.40
7 purchase totals =	$676.23		$729.8710	$729.88	$729.90	$729.90