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	$21.58	13.714%	$24.5395	$24.54	$24.55	$24.50
Purchase #2	$160.72	13.724%	$182.7772	$182.78	$182.80	$182.80
Purchase #3	$68.92	3.340%	$71.2219	$71.22	$71.20	$71.20
Purchase #4	$246.27	6.363%	$261.9402	$261.94	$261.95	$261.90
Purchase #5	$77.32	10.870%	$85.7247	$85.72	$85.70	$85.70
Purchase #6	$79.38	13.428%	$90.0391	$90.04	$90.05	$90.00
Purchase #7	$29.98	4.746%	$31.4029	$31.40	$31.40	$31.40
7 purchase totals =	$684.17		$747.6455	$747.64	$747.65	$747.50