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	$75.48	6.594%	$80.4572	$80.46	$80.45	$80.50
Purchase #2	$82.95	13.695%	$94.31	$94.31	$94.30	$94.30
Purchase #3	$223.93	12.398%	$251.6928	$251.69	$251.70	$251.70
Purchase #4	$217.87	10.214%	$240.1232	$240.12	$240.10	$240.10
Purchase #5	$41.84	8.429%	$45.3667	$45.37	$45.35	$45.40
Purchase #6	$245.48	9.599%	$269.0436	$269.04	$269.05	$269.00
Purchase #7	$93.85	7.576%	$100.9601	$100.96	$100.95	$101.00
7 purchase totals =	$981.40		$1,081.9536	$1,081.95	$1,081.90	$1,082.00