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	$163.29	9.103%	$178.1543	$178.15	$178.15	$178.20
Purchase #2	$51.87	9.352%	$56.7209	$56.72	$56.70	$56.70
Purchase #3	$52.55	13.793%	$59.7982	$59.80	$59.80	$59.80
Purchase #4	$112.75	9.222%	$123.1478	$123.15	$123.15	$123.10
Purchase #5	$81.25	4.800%	$85.15	$85.15	$85.15	$85.20
Purchase #6	$7.44	13.830%	$8.469	$8.47	$8.45	$8.50
Purchase #7	$73.51	8.458%	$79.7275	$79.73	$79.75	$79.70
7 purchase totals =	$542.66		$591.1677	$591.17	$591.15	$591.20