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	$15.62	11.638%	$17.4379	$17.44	$17.45	$17.40
Purchase #2	$133.68	7.653%	$143.9105	$143.91	$143.90	$143.90
Purchase #3	$49.36	5.599%	$52.1237	$52.12	$52.10	$52.10
Purchase #4	$59.52	3.301%	$61.4848	$61.48	$61.50	$61.50
Purchase #5	$63.80	6.143%	$67.7192	$67.72	$67.70	$67.70
Purchase #6	$34.80	7.601%	$37.4451	$37.45	$37.45	$37.40
Purchase #7	$145.37	3.576%	$150.5684	$150.57	$150.55	$150.60
7 purchase totals =	$502.15		$530.6896	$530.69	$530.65	$530.60