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	$21.66	8.275%	$23.4524	$23.45	$23.45	$23.50
Purchase #2	$237.30	12.781%	$267.6293	$267.63	$267.65	$267.60
Purchase #3	$63.82	12.831%	$72.0087	$72.01	$72.00	$72.00
Purchase #4	$101.90	9.531%	$111.6121	$111.61	$111.60	$111.60
Purchase #5	$35.34	5.144%	$37.1579	$37.16	$37.15	$37.20
Purchase #6	$200.32	11.524%	$223.4049	$223.40	$223.40	$223.40
Purchase #7	$9.70	5.649%	$10.248	$10.25	$10.25	$10.20
7 purchase totals =	$670.04		$745.5133	$745.51	$745.50	$745.50