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	$38.69	5.610%	$40.8605	$40.86	$40.85	$40.90
Purchase #2	$127.46	12.289%	$143.1236	$143.12	$143.10	$143.10
Purchase #3	$38.52	7.787%	$41.5196	$41.52	$41.50	$41.50
Purchase #4	$206.25	3.138%	$212.7221	$212.72	$212.70	$212.70
Purchase #5	$184.29	3.843%	$191.3723	$191.37	$191.35	$191.40
Purchase #6	$49.71	4.598%	$51.9957	$52.00	$52.00	$52.00
Purchase #7	$154.47	13.757%	$175.7204	$175.72	$175.70	$175.70
7 purchase totals =	$799.39		$857.3142	$857.31	$857.20	$857.30