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	$243.34	6.346%	$258.7824	$258.78	$258.80	$258.80
Purchase #2	$192.61	7.414%	$206.8901	$206.89	$206.90	$206.90
Purchase #3	$151.49	4.509%	$158.3207	$158.32	$158.30	$158.30
Purchase #4	$92.64	5.874%	$98.0817	$98.08	$98.10	$98.10
Purchase #5	$18.55	5.239%	$19.5218	$19.52	$19.50	$19.50
Purchase #6	$240.80	3.282%	$248.7031	$248.70	$248.70	$248.70
Purchase #7	$55.47	7.322%	$59.5315	$59.53	$59.55	$59.50
7 purchase totals =	$994.90		$1,049.8313	$1,049.82	$1,049.85	$1,049.80