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	$45.37	11.173%	$50.4392	$50.44	$50.45	$50.40
Purchase #2	$77.90	12.405%	$87.5635	$87.56	$87.55	$87.60
Purchase #3	$7.37	5.629%	$7.7849	$7.78	$7.80	$7.80
Purchase #4	$76.39	13.352%	$86.5896	$86.59	$86.60	$86.60
Purchase #5	$54.83	13.847%	$62.4223	$62.42	$62.40	$62.40
Purchase #6	$123.46	4.761%	$129.3379	$129.34	$129.35	$129.30
Purchase #7	$151.44	4.689%	$158.541	$158.54	$158.55	$158.50
7 purchase totals =	$536.76		$582.6784	$582.67	$582.70	$582.60