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	$198.76	13.524%	$225.6403	$225.64	$225.65	$225.60
Purchase #2	$139.52	10.701%	$154.45	$154.45	$154.45	$154.50
Purchase #3	$128.76	6.715%	$137.4062	$137.41	$137.40	$137.40
Purchase #4	$223.94	11.418%	$249.5095	$249.51	$249.50	$249.50
Purchase #5	$7.61	4.108%	$7.9226	$7.92	$7.90	$7.90
Purchase #6	$114.30	3.677%	$118.5028	$118.50	$118.50	$118.50
Purchase #7	$74.47	9.772%	$81.7472	$81.75	$81.75	$81.70
7 purchase totals =	$887.36		$975.1786	$975.18	$975.15	$975.10