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	$91.89	13.287%	$104.0994	$104.10	$104.10	$104.10
Purchase #2	$73.69	12.535%	$82.927	$82.93	$82.95	$82.90
Purchase #3	$67.57	11.818%	$75.5554	$75.56	$75.55	$75.60
Purchase #4	$151.97	11.492%	$169.4344	$169.43	$169.45	$169.40
Purchase #5	$45.84	5.747%	$48.4744	$48.47	$48.45	$48.50
Purchase #6	$166.25	6.813%	$177.5766	$177.58	$177.60	$177.60
Purchase #7	$13.25	11.380%	$14.7579	$14.76	$14.75	$14.80
7 purchase totals =	$610.46		$672.8251	$672.83	$672.85	$672.90