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	$174.86	12.522%	$196.756	$196.76	$196.75	$196.80
Purchase #2	$95.86	13.766%	$109.0561	$109.06	$109.05	$109.10
Purchase #3	$11.98	4.817%	$12.5571	$12.56	$12.55	$12.60
Purchase #4	$32.76	10.667%	$36.2545	$36.25	$36.25	$36.30
Purchase #5	$77.76	7.215%	$83.3704	$83.37	$83.35	$83.40
Purchase #6	$52.43	8.739%	$57.0119	$57.01	$57.00	$57.00
Purchase #7	$53.35	10.348%	$58.8707	$58.87	$58.85	$58.90
7 purchase totals =	$499.00		$553.8767	$553.88	$553.80	$554.10