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	$248.55	12.295%	$279.1092	$279.11	$279.10	$279.10
Purchase #2	$207.43	3.860%	$215.4368	$215.44	$215.45	$215.40
Purchase #3	$142.39	10.182%	$156.8881	$156.89	$156.90	$156.90
Purchase #4	$237.25	10.757%	$262.771	$262.77	$262.75	$262.80
Purchase #5	$92.90	7.331%	$99.7105	$99.71	$99.70	$99.70
Purchase #6	$105.31	9.165%	$114.9617	$114.96	$114.95	$115.00
Purchase #7	$138.32	8.748%	$150.4202	$150.42	$150.40	$150.40
7 purchase totals =	$1,172.15		$1,279.2975	$1,279.30	$1,279.25	$1,279.30