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	$72.38	8.655%	$78.6445	$78.64	$78.65	$78.60
Purchase #2	$83.77	4.616%	$87.6368	$87.64	$87.65	$87.60
Purchase #3	$116.32	12.115%	$130.4122	$130.41	$130.40	$130.40
Purchase #4	$222.30	8.649%	$241.5267	$241.53	$241.55	$241.50
Purchase #5	$94.99	11.184%	$105.6137	$105.61	$105.60	$105.60
Purchase #6	$97.78	11.196%	$108.7274	$108.73	$108.75	$108.70
Purchase #7	$160.44	4.635%	$167.8764	$167.88	$167.90	$167.90
7 purchase totals =	$847.98		$920.4377	$920.44	$920.50	$920.30