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	$28.25	11.706%	$31.5569	$31.56	$31.55	$31.60
Purchase #2	$247.32	3.262%	$255.3876	$255.39	$255.40	$255.40
Purchase #3	$38.44	3.405%	$39.7489	$39.75	$39.75	$39.70
Purchase #4	$115.56	12.789%	$130.339	$130.34	$130.35	$130.30
Purchase #5	$172.48	3.334%	$178.2305	$178.23	$178.25	$178.20
Purchase #6	$104.84	9.358%	$114.6509	$114.65	$114.65	$114.70
Purchase #7	$83.32	8.318%	$90.2506	$90.25	$90.25	$90.30
7 purchase totals =	$790.21		$840.1644	$840.17	$840.20	$840.20