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	$113.52	9.588%	$124.4043	$124.40	$124.40	$124.40
Purchase #2	$40.85	4.292%	$42.6033	$42.60	$42.60	$42.60
Purchase #3	$86.60	11.839%	$96.8526	$96.85	$96.85	$96.90
Purchase #4	$129.45	11.209%	$143.9601	$143.96	$143.95	$144.00
Purchase #5	$88.54	12.346%	$99.4711	$99.47	$99.45	$99.50
Purchase #6	$159.92	10.689%	$177.0138	$177.01	$177.00	$177.00
Purchase #7	$80.72	9.569%	$88.4441	$88.44	$88.45	$88.40
7 purchase totals =	$699.60		$772.7493	$772.73	$772.70	$772.80