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	$44.37	12.141%	$49.757	$49.76	$49.75	$49.80
Purchase #2	$74.63	5.172%	$78.4899	$78.49	$78.50	$78.50
Purchase #3	$16.81	9.111%	$18.3416	$18.34	$18.35	$18.30
Purchase #4	$100.75	10.405%	$111.233	$111.23	$111.25	$111.20
Purchase #5	$41.41	7.693%	$44.5957	$44.60	$44.60	$44.60
Purchase #6	$29.28	9.322%	$32.0095	$32.01	$32.00	$32.00
Purchase #7	$149.43	12.808%	$168.569	$168.57	$168.55	$168.60
7 purchase totals =	$456.68		$502.9957	$503.00	$503.00	$503.00