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	$19.41	6.870%	$20.7435	$20.74	$20.75	$20.70
Purchase #2	$141.38	9.496%	$154.8054	$154.81	$154.80	$154.80
Purchase #3	$73.39	7.578%	$78.9515	$78.95	$78.95	$79.00
Purchase #4	$143.60	5.814%	$151.9489	$151.95	$151.95	$151.90
Purchase #5	$49.81	10.224%	$54.9026	$54.90	$54.90	$54.90
Purchase #6	$58.71	5.269%	$61.8034	$61.80	$61.80	$61.80
Purchase #7	$155.72	12.542%	$175.2504	$175.25	$175.25	$175.30
7 purchase totals =	$642.02		$698.4057	$698.40	$698.40	$698.40