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	$141.65	13.166%	$160.2996	$160.30	$160.30	$160.30
Purchase #2	$212.57	6.360%	$226.0895	$226.09	$226.10	$226.10
Purchase #3	$10.32	11.273%	$11.4834	$11.48	$11.50	$11.50
Purchase #4	$17.56	11.618%	$19.6001	$19.60	$19.60	$19.60
Purchase #5	$99.90	4.401%	$104.2966	$104.30	$104.30	$104.30
Purchase #6	$16.52	10.604%	$18.2718	$18.27	$18.25	$18.30
Purchase #7	$43.53	5.131%	$45.7635	$45.76	$45.75	$45.80
7 purchase totals =	$542.05		$585.8045	$585.80	$585.80	$585.90