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	$6.68	10.195%	$7.361	$7.36	$7.35	$7.40
Purchase #2	$57.45	3.613%	$59.5257	$59.53	$59.55	$59.50
Purchase #3	$226.69	12.853%	$255.8265	$255.83	$255.85	$255.80
Purchase #4	$199.94	13.432%	$226.7959	$226.80	$226.80	$226.80
Purchase #5	$205.34	9.268%	$224.3709	$224.37	$224.35	$224.40
Purchase #6	$172.69	4.822%	$181.0171	$181.02	$181.00	$181.00
Purchase #7	$100.56	11.205%	$111.8277	$111.83	$111.85	$111.80
7 purchase totals =	$969.35		$1,066.7248	$1,066.74	$1,066.75	$1,066.70