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	$17.87	9.182%	$19.5108	$19.51	$19.50	$19.50
Purchase #2	$190.72	12.740%	$215.0177	$215.02	$215.00	$215.00
Purchase #3	$36.69	5.219%	$38.6049	$38.60	$38.60	$38.60
Purchase #4	$67.75	7.166%	$72.605	$72.61	$72.60	$72.60
Purchase #5	$7.61	10.795%	$8.4315	$8.43	$8.45	$8.40
Purchase #6	$149.48	3.604%	$154.8673	$154.87	$154.85	$154.90
Purchase #7	$77.72	6.346%	$82.6521	$82.65	$82.65	$82.70
7 purchase totals =	$547.84		$591.6893	$591.69	$591.65	$591.70