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	$58.31	6.772%	$62.2588	$62.26	$62.25	$62.30
Purchase #2	$37.48	13.692%	$42.6118	$42.61	$42.60	$42.60
Purchase #3	$101.92	10.664%	$112.7887	$112.79	$112.80	$112.80
Purchase #4	$56.30	8.546%	$61.1114	$61.11	$61.10	$61.10
Purchase #5	$169.76	4.191%	$176.8746	$176.87	$176.85	$176.90
Purchase #6	$182.46	4.210%	$190.1416	$190.14	$190.15	$190.10
Purchase #7	$171.59	12.534%	$193.0971	$193.10	$193.10	$193.10
7 purchase totals =	$777.82		$838.8840	$838.88	$838.85	$838.90