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	$211.86	6.689%	$226.0313	$226.03	$226.05	$226.00
Purchase #2	$96.91	11.716%	$108.264	$108.26	$108.25	$108.30
Purchase #3	$95.92	4.728%	$100.4551	$100.46	$100.45	$100.50
Purchase #4	$41.39	9.693%	$45.4019	$45.40	$45.40	$45.40
Purchase #5	$50.95	7.619%	$54.8319	$54.83	$54.85	$54.80
Purchase #6	$137.86	9.469%	$150.914	$150.91	$150.90	$150.90
Purchase #7	$244.69	11.525%	$272.8905	$272.89	$272.90	$272.90
7 purchase totals =	$879.58		$958.7887	$958.78	$958.80	$958.80