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	$42.51	6.406%	$45.2332	$45.23	$45.25	$45.20
Purchase #2	$206.98	3.198%	$213.5992	$213.60	$213.60	$213.60
Purchase #3	$127.87	7.142%	$137.0025	$137.00	$137.00	$137.00
Purchase #4	$68.51	11.759%	$76.5661	$76.57	$76.55	$76.60
Purchase #5	$157.88	12.258%	$177.2329	$177.23	$177.25	$177.20
Purchase #6	$104.69	6.579%	$111.5776	$111.58	$111.60	$111.60
Purchase #7	$86.64	3.820%	$89.9496	$89.95	$89.95	$89.90
7 purchase totals =	$795.08		$851.1611	$851.16	$851.20	$851.10