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	$140.68	11.741%	$157.1972	$157.20	$157.20	$157.20
Purchase #2	$61.66	3.498%	$63.8169	$63.82	$63.80	$63.80
Purchase #3	$175.39	5.636%	$185.275	$185.28	$185.30	$185.30
Purchase #4	$91.39	11.407%	$101.8149	$101.81	$101.80	$101.80
Purchase #5	$93.31	8.159%	$100.9232	$100.92	$100.90	$100.90
Purchase #6	$101.83	11.392%	$113.4305	$113.43	$113.45	$113.40
Purchase #7	$128.28	8.404%	$139.0607	$139.06	$139.05	$139.10
7 purchase totals =	$792.54		$861.5184	$861.52	$861.50	$861.50