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	11.337%	$24.1156	$24.12	$24.10	$24.10
Purchase #2	$112.25	10.277%	$123.7859	$123.79	$123.80	$123.80
Purchase #3	$233.72	3.654%	$242.2601	$242.26	$242.25	$242.30
Purchase #4	$103.89	10.162%	$114.4473	$114.45	$114.45	$114.40
Purchase #5	$26.46	7.225%	$28.3717	$28.37	$28.35	$28.40
Purchase #6	$54.28	10.167%	$59.7986	$59.80	$59.80	$59.80
Purchase #7	$33.28	7.621%	$35.8163	$35.82	$35.80	$35.80
7 purchase totals =	$585.54		$628.5955	$628.61	$628.55	$628.60