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	$135.46	11.322%	$150.7968	$150.80	$150.80	$150.80
Purchase #2	$250.55	11.829%	$280.1876	$280.19	$280.20	$280.20
Purchase #3	$75.65	13.492%	$85.8567	$85.86	$85.85	$85.90
Purchase #4	$51.50	5.799%	$54.4865	$54.49	$54.50	$54.50
Purchase #5	$143.34	10.573%	$158.4953	$158.50	$158.50	$158.50
Purchase #6	$228.78	5.565%	$241.5116	$241.51	$241.50	$241.50
Purchase #7	$105.38	4.428%	$110.0462	$110.05	$110.05	$110.00
7 purchase totals =	$990.66		$1,081.3807	$1,081.40	$1,081.40	$1,081.40