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	$243.98	11.286%	$271.5156	$271.52	$271.50	$271.50
Purchase #2	$109.41	13.797%	$124.5053	$124.51	$124.50	$124.50
Purchase #3	$222.97	13.721%	$253.5637	$253.56	$253.55	$253.60
Purchase #4	$125.46	11.339%	$139.6859	$139.69	$139.70	$139.70
Purchase #5	$13.82	10.503%	$15.2715	$15.27	$15.25	$15.30
Purchase #6	$32.55	7.693%	$35.0541	$35.05	$35.05	$35.10
Purchase #7	$73.75	6.348%	$78.4317	$78.43	$78.45	$78.40
7 purchase totals =	$821.94		$918.0278	$918.03	$918.00	$918.10