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	$18.76	13.851%	$21.3584	$21.36	$21.35	$21.40
Purchase #2	$101.56	4.266%	$105.8925	$105.89	$105.90	$105.90
Purchase #3	$21.74	13.706%	$24.7197	$24.72	$24.70	$24.70
Purchase #4	$131.85	9.190%	$143.967	$143.97	$143.95	$144.00
Purchase #5	$249.46	11.309%	$277.6714	$277.67	$277.65	$277.70
Purchase #6	$143.29	7.845%	$154.5311	$154.53	$154.55	$154.50
Purchase #7	$36.84	3.567%	$38.1541	$38.15	$38.15	$38.20
7 purchase totals =	$703.50		$766.2942	$766.29	$766.25	$766.40