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	$212.92	13.152%	$240.9232	$240.92	$240.90	$240.90
Purchase #2	$46.78	7.493%	$50.2852	$50.29	$50.30	$50.30
Purchase #3	$155.51	8.419%	$168.6024	$168.60	$168.60	$168.60
Purchase #4	$160.39	6.698%	$171.1329	$171.13	$171.15	$171.10
Purchase #5	$212.47	6.534%	$226.3528	$226.35	$226.35	$226.40
Purchase #6	$170.78	8.722%	$185.6754	$185.68	$185.70	$185.70
Purchase #7	$43.90	10.265%	$48.4063	$48.41	$48.40	$48.40
7 purchase totals =	$1,002.75		$1,091.3782	$1,091.38	$1,091.40	$1,091.40