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	$51.25	6.722%	$54.695	$54.70	$54.70	$54.70
Purchase #2	$89.65	10.213%	$98.806	$98.81	$98.80	$98.80
Purchase #3	$232.78	4.859%	$244.0908	$244.09	$244.10	$244.10
Purchase #4	$177.77	4.402%	$185.5954	$185.60	$185.60	$185.60
Purchase #5	$78.61	11.379%	$87.555	$87.56	$87.55	$87.60
Purchase #6	$23.29	4.485%	$24.3346	$24.33	$24.35	$24.30
Purchase #7	$127.42	7.133%	$136.5089	$136.51	$136.50	$136.50
7 purchase totals =	$780.77		$831.5857	$831.60	$831.60	$831.60