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	$59.26	10.600%	$65.5416	$65.54	$65.55	$65.50
Purchase #2	$57.74	8.435%	$62.6104	$62.61	$62.60	$62.60
Purchase #3	$38.48	11.167%	$42.7771	$42.78	$42.80	$42.80
Purchase #4	$116.88	6.549%	$124.5345	$124.53	$124.55	$124.50
Purchase #5	$42.71	8.722%	$46.4352	$46.44	$46.45	$46.40
Purchase #6	$132.40	10.250%	$145.971	$145.97	$145.95	$146.00
Purchase #7	$70.76	4.441%	$73.9025	$73.90	$73.90	$73.90
7 purchase totals =	$518.23		$561.7723	$561.77	$561.80	$561.70