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	$72.56	8.687%	$78.8633	$78.86	$78.85	$78.90
Purchase #2	$141.51	7.864%	$152.6383	$152.64	$152.65	$152.60
Purchase #3	$61.69	10.344%	$68.0712	$68.07	$68.05	$68.10
Purchase #4	$100.30	10.852%	$111.1846	$111.18	$111.20	$111.20
Purchase #5	$98.91	5.291%	$104.1433	$104.14	$104.15	$104.10
Purchase #6	$69.62	4.547%	$72.7856	$72.79	$72.80	$72.80
Purchase #7	$180.63	13.318%	$204.6863	$204.69	$204.70	$204.70
7 purchase totals =	$725.22		$792.3726	$792.37	$792.40	$792.40