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	$149.36	4.172%	$155.5913	$155.59	$155.60	$155.60
Purchase #2	$78.83	6.318%	$83.8105	$83.81	$83.80	$83.80
Purchase #3	$167.69	5.794%	$177.406	$177.41	$177.40	$177.40
Purchase #4	$86.47	11.351%	$96.2852	$96.29	$96.30	$96.30
Purchase #5	$139.73	8.466%	$151.5595	$151.56	$151.55	$151.60
Purchase #6	$84.88	8.833%	$92.3775	$92.38	$92.40	$92.40
Purchase #7	$49.93	6.823%	$53.3367	$53.34	$53.35	$53.30
7 purchase totals =	$756.89		$810.3667	$810.38	$810.40	$810.40