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	$24.31	11.798%	$27.1781	$27.18	$27.20	$27.20
Purchase #2	$121.37	12.503%	$136.5449	$136.54	$136.55	$136.50
Purchase #3	$183.86	4.334%	$191.8285	$191.83	$191.85	$191.80
Purchase #4	$222.68	9.695%	$244.2688	$244.27	$244.25	$244.30
Purchase #5	$126.61	4.656%	$132.505	$132.51	$132.50	$132.50
Purchase #6	$198.47	12.619%	$223.5149	$223.51	$223.50	$223.50
Purchase #7	$43.67	11.596%	$48.734	$48.73	$48.75	$48.70
7 purchase totals =	$920.97		$1,004.5742	$1,004.57	$1,004.60	$1,004.50