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	$199.37	12.719%	$224.7279	$224.73	$224.75	$224.70
Purchase #2	$27.40	6.733%	$29.2448	$29.24	$29.25	$29.20
Purchase #3	$27.62	8.441%	$29.9514	$29.95	$29.95	$30.00
Purchase #4	$87.40	3.516%	$90.473	$90.47	$90.45	$90.50
Purchase #5	$243.61	8.667%	$264.7237	$264.72	$264.70	$264.70
Purchase #6	$93.32	13.339%	$105.768	$105.77	$105.75	$105.80
Purchase #7	$39.56	7.689%	$42.6018	$42.60	$42.60	$42.60
7 purchase totals =	$718.28		$787.4906	$787.48	$787.45	$787.50