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	$105.53	10.605%	$116.7215	$116.72	$116.70	$116.70
Purchase #2	$177.67	10.358%	$196.0731	$196.07	$196.05	$196.10
Purchase #3	$151.71	13.636%	$172.3972	$172.40	$172.40	$172.40
Purchase #4	$62.88	11.848%	$70.33	$70.33	$70.35	$70.30
Purchase #5	$31.67	11.540%	$35.3247	$35.32	$35.30	$35.30
Purchase #6	$190.69	13.773%	$216.9537	$216.95	$216.95	$217.00
Purchase #7	$28.72	9.610%	$31.48	$31.48	$31.50	$31.50
7 purchase totals =	$748.87		$839.2802	$839.27	$839.25	$839.30