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	$38.34	11.869%	$42.8906	$42.89	$42.90	$42.90
Purchase #2	$75.62	8.865%	$82.3237	$82.32	$82.30	$82.30
Purchase #3	$120.72	8.680%	$131.1985	$131.20	$131.20	$131.20
Purchase #4	$67.89	10.183%	$74.8032	$74.80	$74.80	$74.80
Purchase #5	$111.85	5.421%	$117.9134	$117.91	$117.90	$117.90
Purchase #6	$128.76	11.710%	$143.8378	$143.84	$143.85	$143.80
Purchase #7	$167.54	4.499%	$175.0776	$175.08	$175.10	$175.10
7 purchase totals =	$710.72		$768.0448	$768.04	$768.05	$768.00