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	$249.34	11.678%	$278.4579	$278.46	$278.45	$278.50
Purchase #2	$103.69	4.689%	$108.552	$108.55	$108.55	$108.60
Purchase #3	$101.57	7.591%	$109.2802	$109.28	$109.30	$109.30
Purchase #4	$14.81	3.633%	$15.348	$15.35	$15.35	$15.30
Purchase #5	$131.62	12.346%	$147.8698	$147.87	$147.85	$147.90
Purchase #6	$108.55	9.644%	$119.0186	$119.02	$119.00	$119.00
Purchase #7	$18.30	3.165%	$18.8792	$18.88	$18.90	$18.90
7 purchase totals =	$727.88		$797.4057	$797.41	$797.40	$797.50