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	$108.70	7.127%	$116.447	$116.45	$116.45	$116.40
Purchase #2	$119.93	9.251%	$131.0247	$131.02	$131.00	$131.00
Purchase #3	$39.90	5.591%	$42.1308	$42.13	$42.15	$42.10
Purchase #4	$113.33	4.780%	$118.7472	$118.75	$118.75	$118.70
Purchase #5	$128.35	11.850%	$143.5595	$143.56	$143.55	$143.60
Purchase #6	$242.39	4.725%	$253.8429	$253.84	$253.85	$253.80
Purchase #7	$171.55	13.472%	$194.6612	$194.66	$194.65	$194.70
7 purchase totals =	$924.15		$1,000.4133	$1,000.41	$1,000.40	$1,000.30