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	$24.39	4.338%	$25.448	$25.45	$25.45	$25.40
Purchase #2	$92.76	11.839%	$103.7419	$103.74	$103.75	$103.70
Purchase #3	$81.49	9.812%	$89.4858	$89.49	$89.50	$89.50
Purchase #4	$113.89	11.646%	$127.1536	$127.15	$127.15	$127.20
Purchase #5	$119.25	10.793%	$132.1207	$132.12	$132.10	$132.10
Purchase #6	$9.63	10.200%	$10.6123	$10.61	$10.60	$10.60
Purchase #7	$118.25	6.253%	$125.6442	$125.64	$125.65	$125.60
7 purchase totals =	$559.66		$614.2065	$614.20	$614.20	$614.10