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	$57.65	5.434%	$60.7827	$60.78	$60.80	$60.80
Purchase #2	$209.78	13.258%	$237.5926	$237.59	$237.60	$237.60
Purchase #3	$50.81	9.141%	$55.4545	$55.45	$55.45	$55.50
Purchase #4	$124.25	13.150%	$140.5889	$140.59	$140.60	$140.60
Purchase #5	$166.72	10.147%	$183.6371	$183.64	$183.65	$183.60
Purchase #6	$92.93	6.820%	$99.2678	$99.27	$99.25	$99.30
Purchase #7	$189.29	7.710%	$203.8843	$203.88	$203.90	$203.90
7 purchase totals =	$891.43		$981.2079	$981.20	$981.25	$981.30