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	$107.61	6.331%	$114.4228	$114.42	$114.40	$114.40
Purchase #2	$53.83	9.663%	$59.0316	$59.03	$59.05	$59.00
Purchase #3	$131.47	9.472%	$143.9228	$143.92	$143.90	$143.90
Purchase #4	$186.76	12.831%	$210.7232	$210.72	$210.70	$210.70
Purchase #5	$14.85	7.323%	$15.9375	$15.94	$15.95	$15.90
Purchase #6	$74.93	13.708%	$85.2014	$85.20	$85.20	$85.20
Purchase #7	$55.61	7.736%	$59.912	$59.91	$59.90	$59.90
7 purchase totals =	$625.06		$689.1513	$689.14	$689.10	$689.00