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	$121.76	8.694%	$132.3458	$132.35	$132.35	$132.30
Purchase #2	$50.80	10.468%	$56.1177	$56.12	$56.10	$56.10
Purchase #3	$166.30	11.267%	$185.037	$185.04	$185.05	$185.00
Purchase #4	$218.68	5.845%	$231.4618	$231.46	$231.45	$231.50
Purchase #5	$98.94	10.760%	$109.5859	$109.59	$109.60	$109.60
Purchase #6	$177.48	3.719%	$184.0805	$184.08	$184.10	$184.10
Purchase #7	$89.36	3.534%	$92.518	$92.52	$92.50	$92.50
7 purchase totals =	$923.32		$991.1467	$991.16	$991.15	$991.10