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	$108.72	12.724%	$122.5535	$122.55	$122.55	$122.60
Purchase #2	$134.64	13.558%	$152.8945	$152.89	$152.90	$152.90
Purchase #3	$120.33	6.766%	$128.4715	$128.47	$128.45	$128.50
Purchase #4	$83.67	7.136%	$89.6407	$89.64	$89.65	$89.60
Purchase #5	$18.93	3.708%	$19.6319	$19.63	$19.65	$19.60
Purchase #6	$13.49	6.264%	$14.335	$14.34	$14.35	$14.30
Purchase #7	$109.35	4.675%	$114.4621	$114.46	$114.45	$114.50
7 purchase totals =	$589.13		$641.9892	$641.98	$642.00	$642.00