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	$47.34	8.866%	$51.5372	$51.54	$51.55	$51.50
Purchase #2	$9.70	4.730%	$10.1588	$10.16	$10.15	$10.20
Purchase #3	$24.37	10.860%	$27.0166	$27.02	$27.00	$27.00
Purchase #4	$69.39	12.391%	$77.9881	$77.99	$78.00	$78.00
Purchase #5	$138.61	10.652%	$153.3747	$153.37	$153.35	$153.40
Purchase #6	$215.51	6.498%	$229.5138	$229.51	$229.50	$229.50
Purchase #7	$125.88	4.335%	$131.3369	$131.34	$131.35	$131.30
7 purchase totals =	$630.80		$680.9261	$680.93	$680.90	$680.90