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	$121.38	9.141%	$132.4753	$132.48	$132.50	$132.50
Purchase #2	$97.61	12.462%	$109.7742	$109.77	$109.75	$109.80
Purchase #3	$187.80	5.755%	$198.6079	$198.61	$198.60	$198.60
Purchase #4	$54.69	13.265%	$61.9446	$61.94	$61.95	$61.90
Purchase #5	$26.37	12.263%	$29.6038	$29.60	$29.60	$29.60
Purchase #6	$14.27	10.747%	$15.8036	$15.80	$15.80	$15.80
Purchase #7	$31.92	3.676%	$33.0934	$33.09	$33.10	$33.10
7 purchase totals =	$534.04		$581.3028	$581.29	$581.30	$581.30