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	$28.69	12.527%	$32.284	$32.28	$32.30	$32.30
Purchase #2	$82.93	4.358%	$86.5441	$86.54	$86.55	$86.50
Purchase #3	$49.27	9.126%	$53.7664	$53.77	$53.75	$53.80
Purchase #4	$162.49	5.386%	$171.2417	$171.24	$171.25	$171.20
Purchase #5	$128.78	5.111%	$135.3619	$135.36	$135.35	$135.40
Purchase #6	$116.70	9.259%	$127.5053	$127.51	$127.50	$127.50
Purchase #7	$139.29	8.460%	$151.0739	$151.07	$151.05	$151.10
7 purchase totals =	$708.15		$757.7773	$757.77	$757.75	$757.80