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	$25.72	10.709%	$28.4744	$28.47	$28.45	$28.50
Purchase #2	$48.55	8.826%	$52.835	$52.84	$52.85	$52.80
Purchase #3	$27.56	5.751%	$29.145	$29.15	$29.15	$29.10
Purchase #4	$229.33	13.441%	$260.1542	$260.15	$260.15	$260.20
Purchase #5	$43.70	10.792%	$48.4161	$48.42	$48.40	$48.40
Purchase #6	$86.26	4.442%	$90.0917	$90.09	$90.10	$90.10
Purchase #7	$147.61	4.612%	$154.4178	$154.42	$154.40	$154.40
7 purchase totals =	$608.73		$663.5342	$663.54	$663.50	$663.50