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	$111.92	10.309%	$123.4578	$123.46	$123.45	$123.50
Purchase #2	$33.69	5.438%	$35.5221	$35.52	$35.50	$35.50
Purchase #3	$110.88	12.709%	$124.9717	$124.97	$124.95	$125.00
Purchase #4	$112.60	4.233%	$117.3664	$117.37	$117.35	$117.40
Purchase #5	$211.47	4.723%	$221.4577	$221.46	$221.45	$221.50
Purchase #6	$156.25	13.619%	$177.5297	$177.53	$177.55	$177.50
Purchase #7	$100.56	11.119%	$111.7413	$111.74	$111.75	$111.70
7 purchase totals =	$837.37		$912.0467	$912.05	$912.00	$912.10