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	$13.67	12.272%	$15.3476	$15.35	$15.35	$15.30
Purchase #2	$111.41	4.829%	$116.79	$116.79	$116.80	$116.80
Purchase #3	$73.33	12.433%	$82.4471	$82.45	$82.45	$82.40
Purchase #4	$159.73	13.684%	$181.5875	$181.59	$181.60	$181.60
Purchase #5	$91.86	5.560%	$96.9674	$96.97	$96.95	$97.00
Purchase #6	$18.84	12.718%	$21.2361	$21.24	$21.25	$21.20
Purchase #7	$232.65	4.222%	$242.4725	$242.47	$242.45	$242.50
7 purchase totals =	$701.49		$756.8482	$756.86	$756.85	$756.80