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	$11.67	13.367%	$13.2299	$13.23	$13.25	$13.20
Purchase #2	$195.54	10.741%	$216.543	$216.54	$216.55	$216.50
Purchase #3	$105.59	5.603%	$111.5062	$111.51	$111.50	$111.50
Purchase #4	$144.38	12.778%	$162.8289	$162.83	$162.85	$162.80
Purchase #5	$36.32	9.352%	$39.7166	$39.72	$39.70	$39.70
Purchase #6	$149.77	7.133%	$160.4531	$160.45	$160.45	$160.50
Purchase #7	$83.57	11.739%	$93.3803	$93.38	$93.40	$93.40
7 purchase totals =	$726.84		$797.6580	$797.66	$797.70	$797.60