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	$10.79	8.587%	$11.7165	$11.72	$11.70	$11.70
Purchase #2	$208.96	11.260%	$232.4889	$232.49	$232.50	$232.50
Purchase #3	$237.45	5.433%	$250.3507	$250.35	$250.35	$250.40
Purchase #4	$171.72	13.726%	$195.2903	$195.29	$195.30	$195.30
Purchase #5	$90.82	11.356%	$101.1335	$101.13	$101.15	$101.10
Purchase #6	$226.80	12.800%	$255.8304	$255.83	$255.85	$255.80
Purchase #7	$105.81	5.354%	$111.4751	$111.48	$111.50	$111.50
7 purchase totals =	$1,052.35		$1,158.2854	$1,158.29	$1,158.35	$1,158.30