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	$104.67	6.448%	$111.4191	$111.42	$111.40	$111.40
Purchase #2	$196.78	9.572%	$215.6158	$215.62	$215.60	$215.60
Purchase #3	$98.92	13.252%	$112.0289	$112.03	$112.05	$112.00
Purchase #4	$24.53	4.407%	$25.611	$25.61	$25.60	$25.60
Purchase #5	$65.36	10.322%	$72.1065	$72.11	$72.10	$72.10
Purchase #6	$235.98	9.688%	$258.8417	$258.84	$258.85	$258.80
Purchase #7	$67.79	12.479%	$76.2495	$76.25	$76.25	$76.20
7 purchase totals =	$794.03		$871.8725	$871.88	$871.85	$871.70