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	$242.61	10.711%	$268.596	$268.60	$268.60	$268.60
Purchase #2	$139.83	13.275%	$158.3924	$158.39	$158.40	$158.40
Purchase #3	$62.56	6.675%	$66.7359	$66.74	$66.75	$66.70
Purchase #4	$185.32	9.685%	$203.2682	$203.27	$203.25	$203.30
Purchase #5	$189.96	11.571%	$211.9403	$211.94	$211.95	$211.90
Purchase #6	$149.36	12.756%	$168.4124	$168.41	$168.40	$168.40
Purchase #7	$190.38	5.522%	$200.8928	$200.89	$200.90	$200.90
7 purchase totals =	$1,160.02		$1,278.2380	$1,278.24	$1,278.25	$1,278.20