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	$138.82	8.407%	$150.4906	$150.49	$150.50	$150.50
Purchase #2	$27.52	3.478%	$28.4771	$28.48	$28.50	$28.50
Purchase #3	$36.39	5.661%	$38.45	$38.45	$38.45	$38.50
Purchase #4	$165.81	11.349%	$184.6278	$184.63	$184.65	$184.60
Purchase #5	$22.50	9.651%	$24.6715	$24.67	$24.65	$24.70
Purchase #6	$35.46	10.390%	$39.1443	$39.14	$39.15	$39.10
Purchase #7	$32.87	12.810%	$37.0806	$37.08	$37.10	$37.10
7 purchase totals =	$459.37		$502.9419	$502.94	$503.00	$503.00