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	$166.87	5.831%	$176.6002	$176.60	$176.60	$176.60
Purchase #2	$137.93	10.475%	$152.3782	$152.38	$152.40	$152.40
Purchase #3	$168.73	9.313%	$184.4438	$184.44	$184.45	$184.40
Purchase #4	$60.96	3.154%	$62.8827	$62.88	$62.90	$62.90
Purchase #5	$96.27	9.450%	$105.3675	$105.37	$105.35	$105.40
Purchase #6	$123.30	10.653%	$136.4351	$136.44	$136.45	$136.40
Purchase #7	$9.88	10.228%	$10.8905	$10.89	$10.90	$10.90
7 purchase totals =	$763.94		$828.9980	$829.00	$829.05	$829.00