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	$48.97	12.141%	$54.9154	$54.92	$54.90	$54.90
Purchase #2	$167.32	10.732%	$185.2768	$185.28	$185.30	$185.30
Purchase #3	$147.25	11.649%	$164.4032	$164.40	$164.40	$164.40
Purchase #4	$102.72	10.870%	$113.8857	$113.89	$113.90	$113.90
Purchase #5	$109.71	8.152%	$118.6536	$118.65	$118.65	$118.70
Purchase #6	$83.93	12.559%	$94.4708	$94.47	$94.45	$94.50
Purchase #7	$132.41	5.856%	$140.1639	$140.16	$140.15	$140.20
7 purchase totals =	$792.31		$871.7694	$871.77	$871.75	$871.90