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	$47.92	4.688%	$50.1665	$50.17	$50.15	$50.20
Purchase #2	$78.54	5.510%	$82.8676	$82.87	$82.85	$82.90
Purchase #3	$78.80	8.786%	$85.7234	$85.72	$85.70	$85.70
Purchase #4	$18.60	9.258%	$20.322	$20.32	$20.30	$20.30
Purchase #5	$240.60	7.835%	$259.451	$259.45	$259.45	$259.50
Purchase #6	$59.55	6.341%	$63.3261	$63.33	$63.35	$63.30
Purchase #7	$172.35	9.123%	$188.0735	$188.07	$188.05	$188.10
7 purchase totals =	$696.36		$749.9301	$749.93	$749.85	$750.00