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	$136.40	10.804%	$151.1367	$151.14	$151.15	$151.10
Purchase #2	$129.70	9.334%	$141.8062	$141.81	$141.80	$141.80
Purchase #3	$92.64	13.706%	$105.3372	$105.34	$105.35	$105.30
Purchase #4	$10.84	4.487%	$11.3264	$11.33	$11.35	$11.30
Purchase #5	$21.83	10.597%	$24.1433	$24.14	$24.15	$24.10
Purchase #6	$175.32	7.722%	$188.8582	$188.86	$188.85	$188.90
Purchase #7	$159.87	5.102%	$168.0266	$168.03	$168.05	$168.00
7 purchase totals =	$726.60		$790.6346	$790.65	$790.70	$790.50