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	$58.95	12.371%	$66.2427	$66.24	$66.25	$66.20
Purchase #2	$20.29	13.752%	$23.0803	$23.08	$23.10	$23.10
Purchase #3	$59.45	12.846%	$67.0869	$67.09	$67.10	$67.10
Purchase #4	$224.30	8.417%	$243.1793	$243.18	$243.20	$243.20
Purchase #5	$77.87	3.335%	$80.467	$80.47	$80.45	$80.50
Purchase #6	$113.69	12.104%	$127.451	$127.45	$127.45	$127.50
Purchase #7	$90.85	7.530%	$97.691	$97.69	$97.70	$97.70
7 purchase totals =	$645.40		$705.1982	$705.20	$705.25	$705.30