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	$139.26	11.645%	$155.4768	$155.48	$155.50	$155.50
Purchase #2	$90.27	12.633%	$101.6738	$101.67	$101.65	$101.70
Purchase #3	$100.58	13.382%	$114.0396	$114.04	$114.05	$114.00
Purchase #4	$98.62	13.742%	$112.1724	$112.17	$112.15	$112.20
Purchase #5	$181.54	9.660%	$199.0768	$199.08	$199.10	$199.10
Purchase #6	$78.77	8.533%	$85.4914	$85.49	$85.50	$85.50
Purchase #7	$158.33	9.799%	$173.8448	$173.84	$173.85	$173.80
7 purchase totals =	$847.37		$941.7756	$941.77	$941.80	$941.80